First it was a 72cc Japanese horizontal air cooled four stroke, now it's a 150cc Chinese horizontal air cooled four stroke. It's been around for well over a half century, and it still seems to work rather poorly much of the time.
Husqvarna Motor Swap Background
The Horizontal Honda
The Lifan Clones
The Improved Lifan Motors
The Lifan 125 Husqvarna
The Lifan 150 Husqvarna
2017 Lifan 150 Husqvarna
It was my father Gerald's idea. To put some sort of small Japanese or English four stroke motor in a Husqvarna chassis. I had wanted a small displacement four stroke dirt bike since before I ever even rode a dirt bike, but I had not been inclined to do motor swaps. As soon as my 1991 Husqvarna WMX 610 had completely stopped running in the year 2000 my father had been talking about the possibility of putting some other motor in it. It was also my father's idea to put points on the 610 motor, and that is what I eventually did after seeing that it was possible on the 1980 Kawasaki KZ440. The motor swap idea was put aside for quite a few years.
Then in 2014 when I was messing around with the 1992 Husqvarna TE 350 and the 1991 Husqvarna WXE 350 I ended up with an extra chassis. My father was going to put some sort of smaller motor in one of the extra chassis. We got as far as buying a 2004 Yamaha TTR225 with a kaput carburetor, but the motor swap never happened. I got the 32mm vacuum slide Mikuni carburetor to work like new by gluing the diaphragm back in place. And then I ripped the 32mm vacuum slide Mikuni off entirely and replaced it with my extra 34mm DellOrto. That completely solved the TTR225 carburetor problems, but the CDI ignition system still did not work. The advance curve was just totally wrong.
The problem with the fixed advance curve on the Yamaha TTR225 was that it continued to advance all the way up to 4,500RPM. There have been a few automotive distributors over the decades that had a mechanical advance that continued to advance all the way up to 4,500RPM, and that works fine if the engine rarely if ever revs past 4,500RPM. A giant four inch bore by four inch stroke length automotive gasoline engine might go for years without ever revving past 4,500RPM, so the advance curve continuing to advance all the way up to that 4,500RPM engine speed would not seem like any sort of a problem.
On a small motorcycle engine that normally runs between 3,500 and 7,500RPM though a steep advance curve all the way up to 4,500RPM is not a good idea. The result on the TTR225 was that the engine tended to be overly crisp, or extremely harsh at 4,000 to 5,000RPM and stumbling down at 2,000 to 3,000RPM was sometimes a problem. The Yamaha TTR225 ran best on slow flame front travel speed gasoline, but then it had a very hard time revving past about 6,000 or 7,000RPM. The advance curve just never worked. There was always something severely wrong. I might have been tempted to try to put points on the TTR225 motor, but it just did not seem like a good idea to rip apart a reliable running motor to put a finicky and unreliable ignition system on it.
The fact that the TTR225 motor was also very large and heavy for such a small displacement made it seem all around undesirable. When the opportunity came up to trade it for a running 1986 Husqvarna 400 WR two stroke we jumped on it. So long crappy heavy TTR225.
I had been vaguely aware of the air cooled horizontal Honda motors for a long time. My first motor vehicle was a 1979 Honda ATC 70 that I got when I was six years old, and I quickly learned that it was the same basic motor (but with a different transmission) in the Honda Trail 90 (CT 90). I had wanted a Trail 90 for many years, and I even got a chance to ride one that a friend had borrowed. By the time I was actually ready to get my first dirt bike though I wanted something with more substantial suspension. The Honda Trail 90 and Honda Trail 110 were just strange little old bikes that nobody ever seemed to actually ride. Probably because the suspension was only good for medium speeds on rather smooth roads.
Then when we sailed to New Zealand and Australia in 2009 and 2010 I saw that new Honda Trail 110 bikes were still being sold there. The Honda Trail 90 had been discontinued in the U.S. sometime back in the late 1970's, and the Honda Trail 110 had sold only in small numbers for a few years in the early 1980's.
I had been vaguely aware of the Chinese clones of the air cooled horizontal Hondas back around 2003, but I did not know much about them. They were obviously a copy of the old Honda motor, but I never heard anything else about them. There were a few of them around in the small Chinese "pit bikes", and they were very cheap.
Then one day in 2015 my dad came back from a swap meet with a shiny red Jin Ching pit bike. For only $400 running and apparently in good condition it had seemed like a great deal.
The thing about those pit bikes is that they are just very small. Extremely small! The wheelbase is 36 inches, considerably shorter than on a bicycle, and the 8" wheels are miniscule. Sitting on the seat the handle bars hit my knees. It is far too small.
The funny thing about the Jin Ching pit bike though is that it actually works very well for such a small motorcycle. The suspension is too soft for my 200 plus pound weight, but when it does not bottom it is smooth, comfortable and the hydraulic damping actually does work. The tiny drum brakes work fairly well, and the large seat is very comfortable. The steering head angle is very relaxed, and the thing actually can go amazingly fast for such a short wheel base. And it does go fast, like 45mph! Way too fast for such a short wheel base. It really is extremely excessively small for any sort of elevated speeds. It works best just for running out to the shop building. It really is a "pit bike". The biggest problem is that the bars hit on my knees, which makes it difficult to maneuver around turns.
It is actually a very dangerous little motorbike, as it easily goes far faster than the chassis and suspension can handle. At more than about 25mph the rebound damping is extremely insufficient, and it is tricky to stay in control at the higher speeds in third gear. It is actually not so much that the rebound damping itself is all that bad, but rather the wheelbase is just so short that the bike easily gets out of control at higher speeds. To go fast on that short of a wheelbase would require very aggressive rebound damping, where what it actually has is mild cushy suspension with minimalistic damping.
The Jin Ching did run when we got it, but it had severe problems. One was that the air cleaner was missing. It was a bit tricky to get a big enough air cleaner so that it still ran and made power. Most of the air cleaners were miniscule little things. I was able to find a larger "gauze type" pleated cone filter at a local store. It was for a larger 1-7/8"flange, but it was easily able to squish down to the standard 40mm carburetor flange.
The first problem though was the carburetor jetting. It was set with the needle clip at the middle setting, and it blew black smoke at partial throttle openings. At wide open throttle it leaned out on the main jet and made power, but it would barely run at the in-between throttle openings. I moved the needle clip leaner and leaner down to the leanest clip position, and the motor ran better and better each time. Even at the leanest needle clip position though there was still a rich spot where the engine blew black smoke and did not run well. The problem was that the needle had a concave step in it. That concave shape right in the middle of the functional part of the taper results in a bad rich spot.
To fix the carburetor I took the needle out of my old ATC 70, which has been sitting under the house in need of tires, fenders, and a new top end for decades. While I was at school many years ago my father had loaned it to a friend who used it to haul logs, and judging by the wear pattern on the tires it looks like he had been riding it to town also. When it wouldn't start any more he gave it back. Cranking compression completely gone, fenders ripped off and the tires worn out until the inner tubes stuck out through the holes. I didn't care, as I had quickly lost interest in anything without suspension.
The original Honda carburetor on the 1979 Honda ATC 70 is smaller, with a miniscule little 13mm slide. The Walborow "Designed in Japan" Chinese carburetor on the Lifan 70 in the Jin Ching scooter has a much larger 15mm diameter slide. No wonder the Lifan 70 makes so much more power than the ATC 70. Amazingly though the needles looked like they would be interchangeable. The Honda carburetor has a very small slide, but it is a long and tall slide that uses nearly just as long of a needle.
When I put the Honda needle in the Walborow carburetor it worked great. The huge rich spot at 1/2 throttle was gone, and the mixture control was actually sort of close to working. On the leanest needle clip position the hot rod carburetor is very rich at the first 1/5 throttle opening, and then it gets rather lean from 1/4 to 3/4 throttle opening before richening up again on the main jet. On unusually weak gasoline it stumbles at 1/4 to 1/2 throttle sometimes even when fully warmed up at the leanest needle clip position. With the needle clip in the second position the mixture control is more even all the way across, but it is also rather rich all the way across. Especially down at around 1/5 to 1/3 throttle the engine is very rich, but it does run and it does make power. It seems like a very large difference between the first and second needle clip positions on this little Walboro carburetor with a Honda needle. Gas mileage is an unbelievably poor 90MPG at 20 to 30mph even when it is running well on the leanest needle clip position.
There are actually a number of Chinese companies making clones of the old horizontal Honda motors. The main manufacturer appears to be Lifan but there are a lot of Zongchen motors around also. The manufacturer YX (Yin Xiang) is gaining ground with some new options also. Other names in the buisness are Daytona, PisterPro and Piranha.
Lifan has made a 50cc version like Honda used to, but the 72cc motor with the same 47mm bore and 41.5mm stroke length of the old Honda ATC70 motor is much more common. The Honda 50 was the same motor with the exact same transmission, clutch, primary reduction, crankshaft and connecting rod on the same 41.5mm stroke length, but with a smaller 38.5mm bore.
The Lifan 50 and Lifan 70 motors don't look exactly the same as the old Honda 50 and Honda 70 motors, but essentially all of the motor parts are interchangeable. The Lifan cylinder head casting looks a bit different, but the valves and camshafts are interchangeable. Likewise the Lifan cases look slightly different, but all of the bottom end and transmission parts are interchangeable. The Lifan 50 and Lifan 70 are not just similar to the Honda 50 and Honda 70 engines, they are in fact exactly the same engines.
Honda had offered the same air cooled horizontal motor in several larger displacements as well. The most well known being the 86cc Honda Trail 90 motor. The Honda Trail 90 motor is exactly the same as the Honda 70 air cooled horizontal motors, it is just stroked out to 86cc with a longer 49.5mm stroke length. Again the bottom end is exactly the same, with the same cases, the same main bearings, the same crank webs and the same connecting rod. The crank pin is just farther out for the longer stroke length.
The Honda Trail 110 that replaced the Honda Trail 90 for the 1980 model year is again the same motor. This time just bored out to 107cc with a larger 52.5mm bore diameter on the same 49.5mm stroke length of the Honda Trail 90. Honda apparently also made a 125cc version, but it was available for only one year in the late 1970's and was quickly replaced by the Trail 110.
The first air cooled horizontal four stroke Honda 50 and Honda 70 bikes were sold in the late 1960's, but these were smaller, shorter wheelbase bikes than the later Trail 90 and Trail 110.
All of these Honda motors used centrifical clutches on a manual transmission. The Trail 90 and Trail 110 used four speed transmissions, where the ATC 70 used a three speed transmission. The Trail 90 and Trail 110 were also offered with a high/low range transmission. The high/low range transmission was offered as an option on the Trail 90 bikes of the late 1970's, but then the option disappeared when the Trail 110 was introduced in 1980. For 1981 the high/low dual range "eight speed" transmission was back as standard equipment on the Honda Trail 110.
All of these Honda motors used the same basic cylinder head casting and the same camshaft. The 72cc Honda 70, the 86cc Honda 90, and the 107cc Honda 110 all used the same 23mm intake valve and 20mm exhaust valve. To fit the same cylinder head with the same valve spacing on the smaller 38.5mm bore of the 48cc Honda 50 motor a much smaller 13mm intake valve and 11mm exhaust valve were used.
There are actually two different Lifan 125 motors currently available. The older Lifan 125 with a 52.5mm bore and a 55mm stroke length for a 119cc displacement uses the same cylinder head and same small 23mm intake valve and 20mm exhaust valve as the Honda 70, 90 and 110 motors. The new "racing" Lifan 125 motor uses a square 54mm bore by 54mm stroke configuration with a new "large canal" cylinder head. The new cylinder head is very similar to the old Honda cylinder head, but it has been hogged out with bigger ports, a bigger 27mm intake valve and a 23mm exhaust valve. The irony is that the new big valve cylinder head still fits on the old 52.5mm bore diameter. It is the cylinder head that was supposed to come on the Honda Trail 110 bikes.
It is still the same basic motor, with the same main bearings and the same connecting rod as the original 1960's air cooled horizontal Honda 50 and Honda 70 four strokes. Yes, the same connecting rod, with the same center to center length on the same crank pin diameter. And that crank pin is pretty big, about an inch in diameter, with an approximately 5/8" wide roller bearing. The rod bearing is big enough for perhaps as much as about 400cc of displacement. That's a lot more than the original Honda 50 and Honda 70.
The cases look like they are still interchangeable, and it is still the same basic four speed transmission. There are some big changes though. The new Lifan motors shift up into higher gears, where the old Honda motors shifted down into higher gears. The new Lifan motors are also offered with manual clutches, where the old Hondas all had centrifical clutches.
The square "racing" Lifan 125 has been available for an unbelievably low $300 purchase price, complete with a carburetor and the entire ignition system, and it is advertised as a direct drop in replacement for all older 50, 70, 90 and 110 Honda and Lifan horizontal air cooled four stroke motors.
Also available are some even larger Lifan motors built on the same motor platform with the same "large canal" 27mm intake valve and 23mm exhaust valve cylinder head. One is the Lifan 140, which actually displaces 141cc with a 55mm bore and a 59.5mm stroke length. This is really exactly the same motor as the Lifan 125. The ignition system uses exactly the same parts, the transmission and primary reduction are exactly the same and it uses the exact same clutch. It is exactly the same motor, but the price has been $200 more just to get that 1mm larger piston and the crank pin moved out on the crank webs by 2.75mm. The square 54x54 Lifan 125 and the Lifan 140 are advertised as having the exact same compression ratio, so presumably the compression height of the 55mm piston is considerably shorter than the 54mm piston.
Then there is also a Lifan 150, which uses the same cylinder head, the same connecting rod and the same cases. The Lifan 150 is however somewhat different. It comes with a completely different CDI ignition system, and the clutch and clutch cover are different. The Lifan 150 also comes with an aluminum cylinder, where the Lifan 125 and Lifan 140 use cheaper cast steel cylinders like the Honda motors did. The Lifan 150 is still a four speed transmission with a manual clutch, but the ratios for first and fourth gears are different. Second and third gears are still 1.706:1 and 1.238:1 like on the Lifan 125 and Lifan 140. It is just first gear and fourth gear that are spaced out farther for a larger total spread of ratios on the Lifan 150. For all the upgrades and substantial differences the Lifan 150 has been selling for the same $500 as the Lifan 140.
Again it was my father that kept pushing for some smaller four stroke in one of the Husqvarna chassis. After we got the Jin Ching 70 scooter was when I became aware of the new Lifan 125, Lifan 140 and Lifan 150 motors. They are fairly new I think in just the last few years, but I am not exactly sure how many years.
We still needed a bike though, as I was not about to take a good running Husqvarna race motor out of one of my bikes to install some Japanese/Chinese hunk of junk air cooled motor. We were looking for another Husqvarna in bad need of a motor. I was thinking that something would be bound to turn up eventually, as any old Husqvarna chassis from the 1980's up would seem to work fine. I was even considering the 1992 to 2002 Husqvarnas with the Showa suspension, thinking that something could probably be done to tone down the excessive always on compression damping. I have always been very reluctant to modify suspension valving on bikes that I ride hard and fast, but for a little underpowered cruiser it did not seem like it would be difficult to just chop off a big chunk of the always on compression damping.
There were some mid 1990's Husqvarna 610 bikes advertised really very cheap at around $1000 to $1500 in various states of neglect and disrepair, and I liked the idea of getting some more 610 motor parts also. What it came down to though was that I just seemed to be disinclined to buy more Showa Husqvarna suspension, for any purpose. That one 1992 Showa Husqvarna has been plenty of trouble just itself.
When we saw the shiny new looking 1986 Husqvarna 250 WR for $1000 it seemed perfect. At first I was not entirely convinced that I would want to scrap the 250 two stroke motor, but I had some suspicions that it was not going to be something that I wanted to actually ride. I did give the 1986 250 two stroke a good fighting chance though, I even rebuilt it once after it seized up. See The Husqvarna 250 Two Stroke. When the 250 two stroke seized up that second time though I decided on the Lifan motor swap before I even got back home.
Since we had the Jin Ching scooter with the Lifan 70 motor to measure we were able to get an idea of what the installation would look like. Unfortunately it looked like the horizontal Lifan motor was just a bit too long to fit inside the 1986 Husqvarna two stroke chassis. My father wanted to bend the chassis to make room, but I was in favor of keeping all the Husqvarna parts intact. What I came up with was that the horizontal motor would fit in the chassis if it was tipped up just a bit to be more vertical. My father thought this might not work with the pressure lubricating system, but I was quite sure that these horizontal motors would run fine tipped up quite severely.
It looked like the Lifan 140 or Lifan 150 would be better motors, as the size of the main and rod bearings on the Honda/Lifan motors is really huge. Huge like something that would work on about a 300-400cc motor. The transmission is correspondingly huge also. It is not possible to go up to that much displacement on these motors as the cylinder stud spacing can only support up to about a 60mm maximum bore diameter. Still though it certainly is a case of more displacement working better when the bottom end parts are dramatically oversized. The Lifan horizontal motors use 6mm cylinder studs on a 71mm bolt circle, so a 60mm bore diameter leaves only a 0.10" head gasket sealing surface. A tiny bit more bore diameter around 62mm might be squeezed out, but the material between the cylinder wall and the cylinder stud is then getting very thin at less than 1/16 of an inch.
We picked the Lifan 125 for the first attempt though, simply because $300 was a lot cheaper than $500. As it turned out the project added up to much larger amounts of money, and that $200 savings was quickly dwarfed. Nearly twice as much money for the motor just to get the crank pin moved out 2.75mm did seem like a rip off though, so we started with the cheap $300 Lifan 125.
The really big challenge for the motor swap was moving the drive chain from the right side to the left (wrong) side. My father had long been talking about just flipping the stock Husqvarna wheel over to move the chain to the other side. I thought this might be possible, but neither of us could come up with a good way to actuate the rear drum brake from the other side of the bike. My father kept saying that he could just build a pivot of some kind, but I kept saying that it looked like the chain was in the way. Since no concrete plan developed for actuating the brake on the other side we had to come up with something else. If we had started with a later disk brake chassis flipping the wheel over would have been much more realistic. Since we had a drum brake bike to work with I figured the easy thing to do would be just to install a drum brake rear wheel with the chain on the left side. I just needed an 18" rear wheel with a 15mm axle.
I found a partial list of rear axle diameters for motorcycles, and there were quite a few that were the 15mm size. I was thinking that it would be a Suzuki motocross bike from the early 1980s. When I went to a local motorcycle salvage company they did indeed have some of those Suzuki wheels. The problem though was that they had been popular for quite a while for vintage motocross racing, so the demand had been relatively high. All that was left were some really beat up old wheels that needed lots of work, and the price was pretty high anyway. I would have gone for one of the somewhat beat up Suzuki wheels for $100, but then they found an old 1979 Honda XL185 wheel that was in pretty good condition other than a somewhat rusty chromed steel rim. With a less than perfect chromed steel rim it was essentially worthless, even though the spokes were all in good condition and it ran true. They were happy to part with the useless junk for a very modest price.
All I had to do was make up some custom wheel spacers, which I fabricated out of 3/4" schedule 40 steel gas pipe and big 5/8" washers. I had to cut the stock Honda "de-railer" ring off the 50T sprocket so the wheel would go far enough over to the left of the swing arm, and then I had to also grind down the sprocket mounting bolts a bit to make even more clearance to get the wheel all the way over to the left. In the end I also had to shave the inside of the left swing arm end down a bit to get even more clearance. It was only about 1/32" of material taken off, and those beefy cast aluminum swing arm ends had always looked excessively big and heavy to me anyway.
When the new Lifan 125 showed up the first thing I did was try to estimate the stroke length through the spark plug hole. This was difficult as the spark plug was threaded in at an extreme angle and the end of the unexpectedly long camshaft was in the way also. The estimate was not easy to do, and the accuracy was not great, but I kept getting about 2.1 inches. It seemed that it was indeed the 54mm stroke length.
I also tried to measure the insides of the valve seats to make sure it was indeed the 27mm intake valve and 23mm exhaust valve. The inside of the intake valve seat was seeming to be nearly 24mm in diameter, so obviously it was not the 23mm intake valve.
Next I tried to get some idea of what sort of camshaft was in the motor. I was surprised to find that the duration was very short at about 220 or 223 degrees at 1mm valve lift. On such a small displacement motor the 1mm valve lift spec is actually rather wide. I thought that it might be more realistic to do the duration measurement at 0.03" of valve lift, and that seemed to yield about 227 degrees of duration. A very small camshaft, but not quite as small as I had first thought. These estimates were pretty rough, as I was really just guessing at the 0.030" or 1mm valve lift amount. It was good enough though that I was able to get some idea of what sort of camshaft was in the motor. A very small one really. It looked to be installed straight up with split overlap right at top dead center, and the lobe separation angle seemed to be rather tight at around 108 degrees. I was very worried that it was too small of a camshaft for a 54mm stroke length motor, but I figured we might as well give it a try since it was what came stock from the factory.
Mounting the motor was a bit of a challenge. It was really my father's project, so I worked on other things and let him make up templates for mounting plates. I did offer suggestions from time to time about how I thought the motor should be mounted, and my father tinkered away with drawing first, second and third generation templates, getting closer and closer to a good shape for the plates.
I did some measuring also, and we marked the third set of cardboard templates with what we thought would be close to the final shape. My father cut the pieces out of 0.135" thick plate he bought at a local steel supply company, and then I fit them to the bike and motor and did the final installation.
With the motor mounted up the challenges were not over. The shift lever, brake lever and kick start lever all fit very differently than on either a 1986 Husqvarna or one of the little bikes that the Lifan motors go in. The motor ended up mounted several inches farther forward from the foot pegs than in any of the bikes designed around the horizontal Lifan motors, so this added some considerable difficulties.
A problem that we ran into was that the Lifan 125 motor was actually wider than the Husqvarna motors. Both the '86 400 two stroke and the 1991 610 four stroke are a maximum of 10-1/2 inches wide, and that is at the ignition cover which is rather far forward and out of the way on the right side. At the sprocket cover near the brake pedal the Husqvarna motors are only 9-3/4 inches wide. Much narrower than the 11 inch wide Lifan 125 motor.
The way that the Lifan motor mounted in the Husqvarna chassis was with the center line of the cylinder very close to the center line of the frame. This resulted in the sprocket being as far to the right as possible, while still allowing sufficient clearance for the chain to run back along the swing arm. The left side of the Lifan motor is tucked in fairly well, with the ignition cover bulging out only slightly. On the right side though the Lifan 125 has this big clutch cover that just sticks way out there. It seems like the clutch cover sticks out much farther than it needs to, but this is the result of a rather sloppy conversion from a centrifical clutch to a manual clutch. The Lifan 125 uses the same basic clutch cover size and shape for both the semi-auto and manual clutch versions, so this means that there is just a bunch of clutch cover unnecessarily sticking out on the manual clutch Lifan 125.
The kick start shaft ends up sticking out rather in the way of the right hand foot peg, and then the foot peg is in the way of the kick start lever. The solution for the kick starter was to mount the lever rather far forward, and this required shaving some off of the irrationally fat and unbelievably heavy 330g cast steel kick start lever so that it would clear the even wider forward part of the clutch cover.
The next problem was that there was no room at all for the stock Husqvarna brake lever to go forward over the foot peg, the kick start shaft and clutch cover are totally in the way. An entirely custom rear brake pedal going under the foot peg was required. I made this out of the same 0.135" mild steel plate with a bent tab on the end for a tip. It was actually quite a challenge figuring out how to snake the brake pedal under the foot peg and then forward past the lower frame rail. Then the tip of the pedal had to be far enough out to the right so that it was not completely blocked by the clutch cover sticking out. It was possible though and it turned out well. I was able to hook the stock 1986 brake cable up between my custom peddle and the Honda brake plate.
I also fabricated a mounting plate to install the Lifan ignition coil on the frame bracket where the stock Spanish Motoplate coil/control module had been mounted.
For an exhaust system we ordered a "Project Bike" header pipe to get the mounting flange and first bends. Our first attempt was a rather ugly thing made up with some 1-1/4" chromed brass plumbing fittings for elbows. It worked, but when we tried to put the 1986 enduro gas tank on it did not fit. I had not been worried about the tank clearing as we had two smaller plastic Husqvarna motocross tanks that did not stick down so far. These had come with the 1986 Husqvarna 250 WR, and I had not looked at them much. When I tried to mount one to the 1986 frame though I found that they are actually 1984 Husqvarna tanks, and they don't go on the 1986 frame at all.
I did stick one of these 1984 tanks on with no seat just to fire the new Lifan 125 Husqvarna up for some test rides. Later I built another exhaust system by bending 1" mild steel tubing and welding it to the first turn of the "project bike" header. This dumped into the stock 1986 Husqvarna muffler, which my dad mounted to the right hand side of the bike with some custom bending of the stock air box mounting tap on the sub frame.
The Lifan 125 had come with a 14 tooth 420 front sprocket, but I ordered a 15 tooth 428 front sprocket to go with the 50 tooth 428 sprocket on the Honda XL185 rear wheel. When I measured the primary reduction ratio I got 3.70:1. The ratios of the four gears were published in the specs for the engine, but the primary reduction ratio had been left a mystery. With a 0.96 overdrive fourth gear the 15/50 gearing works out to 9,200RPM at 60mph.
The Lifan 125 had been advertised as coming with a 22mm "racing carburetor". When we got the motor what was in the box was a much smaller carburetor with a 17mm slide. The carburetor opening was somewhat taller, but it was also narrower even than the 17mm slide. The result was that the opening had the same cross sectional area as a 19mm carburetor. This was disappointing, as I knew the 125 four stroke was going to need more carburetor than this. I complained to the company I bought the Lifan 125 motor from, but they insisted it was really a 22mm carburetor. This went back and forth for a while getting nowhere, so I ordered a "27mm" carburetor for the unbelievable low price of just $18. When this "27mm" carburetor showed up it turned out to be a 24mm carburetor, which seemed just right. It mounted up to the same 26mm intake manifold just like they were designed to go together.
The way the engine went in the 1986 Husqvarna chassis it ended up tilted back about 20 degrees. My father thought this would cause problems with the carburetor, but again I was quite sure that slide type carburetors would work just fine on rather extreme angles. I had after all never had any trouble with ridding wheelies on dirt bikes, and that ends up with much more than a 20 degree angle. Thinking that we could always build some sort of custom intake manifold to tilt the carburetor back down I did not worry about it much.
For an air filter we started out with a little pleated "gauze" type cone filter similar to what I put on the 72cc Jin Ching scooter. This worked, but later we switched to a 4" Uni foam pod filter that has a much larger capacity.
When I first fired the Lifan 125 up with the 24mm "27mm" carburetor it did not run well at all. It blew black smoke, and fouled the spark plug badly. I thought the carburetor was jetted extremely too rich. When I took it apart I found that the pilot jet was not marked. The mystery pilot jet was obviously somewhat bigger than the 38 size pilot jet out of the ATC 70, but I did not know how much bigger. I stuck the 38 pilot jet on the end of the unmarked pilot jet and fired the engine up again. This time it ran and idled fairly well and did not fowl the plug. When I tried to ride it though it would not take more than about 1/4 throttle opening. At wider throttle openings it just got supper rich and would not run.
It was only when I took the carburetor off to put the stock carburetor back on that I found that I had been running it with the choke stuck on. Boy, that was stupid.
That reminds me of one time when I was 13 years old when I completely disassembled the carburetor and fuel system on my Honda ATC70 just to discover that there was no gasoline in the gas tank. Boy, that was stupid. There is however an explanation for this seeming stupidity. A few times before when the ATC70 wouldn't start, or wouldn't run as small throttle openings I had found a small amount of granular material in the bottom of the carburetor bowel and blowing through all the little orifices had gotten the machine running again. When the ATC70 wouldn't start, but had a strong spark and normal cranking compression, I went right to the carburetor. I took the bowel off, and the gasoline level was low. I checked the needle and seat, and it was sealing and there was no obstruction through to the fuel line. I turned the petcock on, and no gasoline came out. I disassembled the petcock and still no gasoline came out. Finally I looked in the tank, and it was dry as a bone! This might be the first time I ever found evidence of disappearing gasoline, as I was quite sure that I hadn't ridden the ATC enough to get anywhere close to using up that tank of gas. I always did wonder how such a small and slow vehicle could use so much gasoline, but that time it seemed that it had used several times more even than it's normal high consumption rate. Interestingly it was not long after that incident with disassembling the ATC70 carburetor to discover the gas tank was dry that I got my 1987 Honda CR125 race bike, and that thing was even more of a fuel hog.
When I tried the stock 19mm "22mm" carburetor the Lifan 125 ran pretty well, with amazingly strong low end torque for a such a small four stroke. What was also amazing was that the little 54mm stroke length engine was not getting harsh at any lower engine speeds, just smooth and powerful torque all the way through. The torque was great, but the power went flat extremely early and it did not actually make more power than the Lifan 70 in the Jin Ching scooter. As I had expected the 19mm carburetor was far too small.
I then put the 24mm "27mm" carburetor back on and the Lifan 125 made slightly more torque even than it had with the small 19mm "22mm" carburetor. The midrange torque was improved very slightly, but the top end power was like twice as much. Obviously it wasn't actually twice as much power, but it sort of felt like twice as much. The Lifan 125 still seemed to go very flat up at the top of the engine speed range, but it revved higher and made a lot more power than it had with the smaller carburetor. Yes, the stock carburetor was too small.
Thinking that perhaps the difference was in the jetting I put the stock 19mm "22mm" carburetor back on again and did some main jet modification. The stock main jet in the 19mmm "22mm" carburetor was an 83 and it was the same thread size as the main jet out of the ATC70. I drilled the ATC70 main jet out to the smallest drill near that size I had, which was 0.039" in diameter and yielded a 98 size main jet. That was a huge difference, and the engine would barely run with such a rich mixture. At first it would not run at all above about 1/2 throttle, but then once fully warmed up on some big pulls I could get the throttle wide open with the engine pulling on the top end. Power was about the same as it had been with the 83 main jet, it just ran much more poorly. A size 85 or 87 main jet might have worked better, but it seemed clear that the dramatic difference in power was due to the carburetor size and not the jet size.
When I put the 24mm "27mm" carburetor back on I messed around with different needle clip positions. I found that the engine ran better with more instant torque with the needle clip on the second position instead of the third position it had come set at. I also went down to the first needle clip position, and this also worked rather well. At the first needle clip position though there were sometimes severe stumbling problems at lower engine speeds. The main jet seemed fine, but I did not know what size it was. The marking was cut out by the screw driver slot so that all that was left was a "9" and part of either a "3" or a "5". I was not sure if it was a 93 or a 95 size main jet, but it did work.
When I put a timing light on the engine I found the source of the stumbling. It was a stupid advance setup. The CDI control box that came with the Lifan 125 is a very simple and very cheap $8 part. It does not have any advance curve, instead it has an all-at-once advance. This could work fine, especially on a small bore engine that has no need for large amounts of spark advance. The problem was that the amount of all-at-once advance was extremely excessive. It was a massive nine degrees of crankshaft rotation that came up at about 3,200RPM. That is a huge change in spark timing for a 54mm bore engine, and that was obviously what was causing the intermittent stumbling around 2,500 to 3,200RPM. The stock spark timing was marked on the flywheel as 27 degrees BTDC, but the Lifan 125 came set with 25 degree BTDC spark timing. This resulted in a starting and idling spark timing of 16 degrees BTDC, which was carried all the way up to the point of all-at-once advance at 3,200RPM.
Small bore engines are however very easy to tune in full flame front travel mode. A 54mm bore engine does not need much spark advance to run in full flame front travel mode, and larger amounts of spark advance up to about 20 degrees BTDC can be well tolerated in full flame front travel mode if the compression ratio is low enough. The result was that the huge 9 degrees of all-at-once advance could sort of be made to work if the combustion properties of the gasoline were matched just right to the motor and the ignition system. The Lifan 125 did actually sort of work much of the time, which was amazing. To be honest I wouldn't have expected 9 degrees of all-at-once advance at 3,200RPM really to work at all, even in a little 125cc engine. I would have expected 9 degrees of all-at-once advance at 3,200RPM to cause either huge amounts of harshness at 3,200 to 3,700RPM or horrible weakness and stumbling at 2,500 to 3,200RPM. Or both.
On normal gasoline the little 54mm stroke length engine did get somewhat harsh around 3,200 to 4,000RPM, but this is not at all unusual for two inch stroke length engines. The 25 degree spark timing is way out on the early end of what has any chance of working, and 25 degrees BTDC really is too early for a 125cc motor. The Husqvarna 610 motors have often been noticeably considerably harsher and less powerful from 3,500 to 4,500RPM at 25 degrees BTDC than at 23 degrees BTDC. The 25 degree BTDC spark timing can sometimes be made to work even down to 3,000RPM, but it is way out on the early end of the spark timing values that are capable of hitting the latest possible time of late compression ignition. A bit later spark timing around 21 to 23 degrees BTDC much more reliably hits the latest possible time of late compression ignition, and in the very small 125cc motor 25 degree BTDC spark timing results in a large amount of the gasoline burning in flame front travel combustion before late compression ignition takes place. This causes some harshness even if the latest possible time of late compression ignition can still somehow be hit. Later spark timing around 18 to 23 degrees BTDC would tend to be much smoother and even more powerful around 3,500 to 5,000RPM in the 125cc motor, but what was happening instead was that I was getting mostly very weak low temperature of combustion potential gasoline. On this unusually weak gasoline even the short 54mm stroke length and rather early 25 degree BTDC spark timing was not harsh at all.
It was not the weakest coldest burning gasoline I have ever seen, no when I swapped it into the Husqvarna 610 motors it did sort of work. I could tell it was somewhat low temperature of combustion potential gasoline as the 610 motors and my 386 stroker motor all were a bit whiny with some little bits of surging around 4,500 to 5,500RPM, and harshness around 3,000RPM was for the most part totally absent. It was around 4,500 to 5,000RPM that the three inch stroke length 610 motors were surging a bit, and it was up at 5,000 to 5,500RPM that the 2.68" stroke length 386 stroker motor was surging a bit. The surging was rather slight though, and all of the Husqvarnas were running and making fairly reasonable power to around 8,000RPM when I swapped the same gasoline back and forth with the Lifan 125. On gasoline straight from the gas station the bigger Husqvarna four strokes were sometimes running better, with no surging and more power to somewhat higher engine speeds.
What I quickly found was that the unmarked pilot jet in the 24mm "27mm PZ27 HS Japan" carburetor was on the small side. Often the engine would stumble horribly at all lower engine speeds at the first crack of the throttle. I tried parking the bike on a steep downhill to see what difference the angle would make, and I did notice some very slight difference. The thing was though that the engine was still stumbling at those small throttle openings around 1/8 throttle even when parked on an extreme downhill. It just was not stumbling quite as bad as when parked on flat ground.
Right away when I started using the 24mm "27mm" carburetor I had added a piece of fuel hose stuck over the end of the pilot jet as an extension. The pilot jet is towards the front of the carburetor, and it does not stick down nearly as far as the main jet. This meant that with the carburetor tipped back the pilot jet rather easily came out of the fuel in the carburetor bowel. The engine did run with the stock carburetor, but it was obviously sucking air in the pilot jet. The pilot jet extension solved the air sucking problem, but the pilot jet itself was still giving trouble.
I even switched from a piece of rubber hose to a soldered on brass tube as an extension to eliminate any possibility of leaks, but the pilot jet was still giving trouble. The angle of the carburetor did make some small difference, but it was very slight. The fact that the engine sometimes would not even run at small throttle openings when parked on an extreme downhill indicated worse problems than just the angle of the carburetor.
Sometimes the engine stumbled at the first crack of the throttle all the way down to low idle, but other times it stumbled only up around 2,500 to 3,200RPM. When the stumbling was happening at all engine speeds, all the way down to low idle, there was obviously a pilot jet problem.
When I swapped gasoline back and forth between the Husqvarna motors and the Lifan 125 I found that although the gasoline that caused stumbling in the 24mm "27mm" HS Japan equipped Lifan 125 was unusually weak and low energy density it did run in the DellOrto equipped bikes. Even the 12.2:1 hot rod 610 motor with the needle clip at the leanest position running only 17 degree BTDC spark timing always ran without stumbling or any cutting out at any engine speed, and most of the time it was running and making power to 8,000RPM without difficulty. A few times on very weak gasoline I have gotten some stumbling around 4,500 to 6,000RPM with the 17 degree BTDC spark timing setting on the 12.2:1 hot rod 610 motor when it is first fired up cold, but this goes away once the engine is fully warmed up. Or is that when the garbage in the carburetor bowel has been used up and replaced with gasoline from the tank? Sometimes it is hard to tell the difference without draining the carburetor bowel before starting the motor. I had always wondered why so many bikes had those drain fittings on the carburetor bowels.
Part of this is that the aluminum points mounting plate I have on the 12.2:1 hot rod 610 motor actually changes shape as it warms up. The cold static timing setting is 16 degrees BTDC, but once the engine warms up the static timing setting advances to 17 degrees BTDC. I have checked this many times, the static timing setting is always about one degree earlier when I measure it with the motor fully warmed up. This is true whether the static timing setting is at 17 degrees BTDC or 27 degrees BTDC. It is always a one degree difference between cold and fully warmed up. I always consider the static timing setting to be the warmed up value, as that is what the engine actually runs with the vast majority of the time. The one degree change is from a cold plate at say a 70 degree ambient temperature up to a hot plate at about 180 degrees Fahrenheit that burns my fingers if I touch it for more than a second. The warmed up static timing setting does not appear to change significantly based on how hard the engine is run. The difference between the ambient temperature up to the operating temperature is very large compared to the variations in operating temperature as the engine is run harder or cruised more casually. I do notice though that if I go for just a very short test ride that does not get the oil fully heated up then the static timing setting ends up a very small bit less advanced. Perhaps it is 0.75 degrees of advance on a short 2 mile test ride, versus 1.25 degrees of advance once the oil is fully warmed up on a longer ride with lots of aggressive high speed acceleration. When I was being forced to run large amounts of spark advance around 26 to 28 degrees BTDC all the time I liked the advancing effect of the aluminum points mounting plate. The engine was a bit milder and smoother when first fired up but had more lag, and then only once fully warmed up did the engine run sufficiently crisply with less lag but also with more harshness due to the spark timing being earlier than 25 degrees BTDC.
The 24mm "27mm" HS Japan carburetor obviously just had a small pilot jet that was yielding a leaner mixture. The stock unmarked pilot jet seemed to be just about big enough to work on normal gasoline, but I was not getting much of that. Sometimes when I brought gasoline straight home from the gas station the Lifan 125 Husqvarna worked fairly well, even with the needle clip in the leanest position. Other times though the gasoline that came straight from the gas station would barely work, and pretty much every time I left gasoline unattended overnight it would not work at all the next day with that small pilot jet.
One day when the engine would hardly run at all bellow 3,200RPM with the needle clip in the leanest position I took a 14 mile gas mileage test ride on a mostly flat road with mostly only larger sweeping turns. I put a measured amount of gasoline into the empty tank using an oil can with mostly parallel sides and nice graduations on a clear plastic strip. I cruised at the fastest speed that felt like it was not reducing gas mileage. I timed the 14 mile loop, and found that I had cruised at about 33mph, which would be 5,000RPM. I drained the remaining gasoline back into the graduated oil can, and I had used just slightly over one pint for about 102MPG. I had expected better mileage from the Lifan 125. Part of the problem was that the gearing was actually still too low. I cruised at less than 1/4 throttle, and there was more power to accelerate to much higher speeds. There was some bad vibration at about 6,000RPM, but then this cleared up at higher engine speeds and the bike kept accelerating. This on such weak gasoline that it was just stumbling horribly and would barely run at any engine speeds from 2,000 to 3,200RPM. Up above 3,200RPM though the engine ran seemingly just fine at any throttle openings. It was able to accelerate up somewhat past the vibration around 6,000RPM, but top speed was not seeming as high as I had expected either. I don't think it was getting much above 50mph.
I had expected higher mileage for a few different reasons. One was that the 72cc Jin Ching scooter geared very low with the dramatically oversized bottom end and transmission parts is very inefficient. I expected that more displacement on the same bottom end and geared higher would do a lot better. The Lifan 125 did do better, delivering higher gas mileage at higher speeds than the Jin Ching cruises at. The difference was however smaller than I had expected. I also expected better mileage based on the 140MPG at 31mph (175MPG UK at 50kph) that the Honda Trail 110 was apparently rated to deliver.
Going back up to the second needle clip position got the Lifan 125 to run with little to no stumbling much of the time at 2,500 to 3,200RPM, but then there was just horrible stumbling nearly all the time at the first crack of the throttle at all lower engine speeds all the way down to low idle. Even once the engine was fully warmed up on a balmy 70 degree mid October day the stumbling at the first crack of the throttle continued to be somewhat of a problem. Again parking the bike on a steep downhill reduced the stumbling somewhat, but the stumbling did not go away. One time even on gasoline straight from the gas station, with the engine fully warmed up on a warm afternoon and the bike parked on a steep downhill there was still considerable stumbling at around 1/8 throttle. The pilot jet was seeming too small.
As a first step I drilled the unmarked pilot jet out with a "0.5mm" twist drill. The "0.5mm" drill actually measured 0.0182" in diameter on the drill stock end, so the jet I ended up with seemed like it was about the 46 or 47 size. This got the 24mm "27mm" carburetor to run, but it was obviously very rich at the first twist of the throttle. I also went back up to the second needle clip position, and the bike was running even if it felt extremely too rich at the fist twist of the throttle.
I then ordered a "26mm" carburetor kit that looked like all the same pieces as the 24mm "27mm" HS Japan carburetor. The kit was very cheap at $9 delivered, and it came with not only a pilot jet, main jet, needle and needle jet and needle and seat but it also came with all of the gaskets, seals and O-rings as well as new floats and even a new idle screw and spring. A very complete carburetor kit for a very low price.
When I got the kit I was amazed to find another unmarked pilot jet, but it did look bigger than the pilot jet that had come with the 24mm "27mm" HS Japan carburetor. When I put this new pilot jet in the 24mm "27mm" carburetor it worked well. The stumbling was gone, and the excessive rich feeling at the first twist of the throttle was also gone. Sometimes I still got stumbling at 2,500 to 3,200RPM, but that was the result of the huge 9 degrees of all-at-once advance coming up there at 3,200RPM. Amazingly the engine ran much of the time without the 9 degrees of all-at-once advance causing anything more than a slight and hardly noticeable flat spot around 3,000RPM.
When I tried the 92 size main jet out of the PZ26 kit it at first worked exactly the same. The 92 jet looked exactly the same as the poorly marked jet that came with the PZ27 carburetor, so I thought one was a 92 and one was a 93. Then a few days later the gasoline I had turned to crap and the engine started stumbling at large throttle openings. For some reason I thought I wanted to keep the very slightly smaller 92 main jet for when the gasoline went back to normal, so I drilled out the poorly marked 93 or 95 main jet to the 98 size with the 0.0388" diameter number 60 drill. I ran the drill through by hand just till it came out the other side. When I tried the 0.0388" diameter drill stock end in the hole it would hardly go in at all. Only the endmost bit of the drill stock end that measures 0.0386" would start into the drilled hole. This was certainly smaller than a 99 size, actually a 98 size.
The motor again ran and made power with the drilled out main jet, but it felt much too rich at wide open throttle. Then the gasoline started to get even weaker, and the engine was sometimes hardly able to run when cold and severely lacked power once fully warmed up. Getting gasoline straight from the gas station, or even just taking a quart of gasoline out of one of the Husqvarna four strokes got the Lifan 125 to run reasonably well. Once the gasoline sat unattended in the tank for a few days though it often would not work, even once the engine was fully warmed up after several miles of riding.
On an only slightly chilly late November afternoon with the ambient temperature at 46 degrees I took a little test ride at 1,000 feet of elevation with a handheld chart plotter in my left hand to measure the speed over ground of the Lifan 125 Husqvarna. This was with the needle clip in the second position and the big drilled out 98 size main jet in the 24mm "27mm" HS Japan PZ27 carburetor. The little 125 thumper was running fairly well, although it was seeming slightly weak. There was no hint of any harshness at any lower engine speeds, and the engine was pulling right up without really any stumbling. Just a bit of a flat and chugging feeling at around 2,500 to 3,000RPM. In second gear the engine pulled hardest at 27 to 34mph, which with the 15/50 gearing is 7,700 to 9,700RPM. I was able to hit 38mph several times on flat ground in second gear, but the power was dropping off up there quite severely. That would be 10,900RPM at 38mph in second gear, which the engine did with ease. The power was just going very weak above 10,000RPM. In third gear it pulled to 46mph with ease, which would be 9,200RPM. In fourth gear the bike accelerated nicely all the way up to 45mph and 50mph, but it took it's sweet time doing it. That 50mph in fourth gear is 7,700RPM. It seemed to have a lot more to go also, but I kept running out of straight always. I suspect that the Lifan 125 Husqvarna will be able to pull up to about 60mph with the 15/50 gearing, which would be an engine speed of 9,200RPM.
It seems that the way the Lifan 125 runs on this weak and somewhat low temperature of combustion potential gasoline is to hit the earlier and easier to hit 5 degree ATDC time of late compression ignition from about 7,500 to 10,000RPM. Down at lower engine speeds it is the latest possible time of late compression ignition, which is sometimes carried all the way down to the 3,200RPM advance curve shoulder. Other times it seems like it is just full flame front travel mode up a bit higher to about 4,000RPM. Sometimes the engine barks hard at the earlier and easier to hit 5 degree BTDC time of late compression ignition down to somewhat lower engine speeds around 6,000RPM. At less than about 7,000RPM the earlier and easier to hit time of late compression ignition certainly can seem somewhat loud and harsh on the two inch stroke length engine, but it usually also delivers a bit more torque down to about 6,000RPM.
There has never been the slightest bit of whining or surging from the little Lifan 125 motor at any engine speed, even on gasoline that does cause some considerable surging in the 2.68 inch stroke length 386 stroker motor around 5,000 to 6,000RPM. The severely low temperature of combustion potential gasoline that was causing extreme levels of surging and whining in the 386 stroker motor and in the 610 motors has not showed up at all in the months that I have been running the Lifan 125.
There are two things that have surprised me quite a bit about how the Lifan 125 has been running. One is that it is so often able to run smoothly and powerfully all the way down to the 3,200RPM advance curve shoulder. The other very surprising thing is that such a short duration camshaft with such an early intake valve closing time delivers maximum power up in the 7,500 to 9,500RPM range of engine speeds. The fact that it is a small 125cc engine with a small 27mm intake valve does mean that the duration at 1mm valve lift is perhaps not quite the same as for a 500cc/cylinder displacement with 40mm intake valves. Perhaps the duration at 0.030" valve lift on the 125cc engine would be more directly comparable to a the duration at 1mm valve lift on larger motorcycle engines. At 0.030" valve lift the duration of the Lifan 125 camshaft is a bit longer, perhaps 227 degrees. Still I would have expected that little camshaft to deliver maximum cylinder filling down in the 3,500 to 6,000RPM range of engine speeds. Obviously cylinder filling is however staying fairly high to 8,000 and 9,000RPM, no doubt thanks to the aggressive fast closing intake valve ramp allowed by ratio rockers on the single overhead camshaft.
The Lifan 125 Husqvarna project was a smashing success, and we have both found it to be our favorite bike to ride around. Very quickly my father suggested that I order a Lifan 150 to see how that motor would work out. Or perhaps he just wanted his Lifan 125 all for himself. In any case we were both exited about another Lifan Husqvarna build. By this time the extra $200 on the purchase price was seeming insignificant, and I was ready to give the bigger motor a try. The problem though was that I needed another bike to put it in. As much fun as the Lifan 125 Husqvarna project had been I was not about to rip one of the real Husqvarna open class motors out of a bike to replace it with a hunk of junk air cooled Chinese motor.
I began looking for another Husqvarna. There were some older and very incomplete 1978 to 1983 dual shock bikes advertised for just a few hundred dollars, but not particularly close by. There was another nearly entirely complete 1986 Husqvarna 400 WR for sale cheap, but I knew I would just have to fix that one up and ride it as a second 400 WR. There was no way I was going to throw away a 400 two-stroke motor to replace it with a crappy little Chinese air cooled engine. I was about to buy the '86 400 WR just to have a second one of those and forget about the Lifan 150 Husqvarna project, but then I saw an ad for some disassembled Husqvarna bikes.
The guy that had them said it was a 1984 and a 1985, but the picture of the 1985 looked to me like a 1986 500 two stroke and it was mostly complete. In one of the pictures I could see a disassembled and very incomplete 1986 sitting in the back behind some other parts. I asked if the other '86 was for sale and how much, and the guy rather cryptically responded that I could have both of them for $750. He was not specific about which two of the three bikes he was talking about.
Since $750 for one mostly complete Husqvarna and another frame sounded like a great deal I headed over to buy them. The other frame was a 1986 Husqvarna, and the 250 two stroke motor went with it. It was just a frame, forks, front wheel, front brake system and motor. No swing arm, linkage or shock. The other bike was indeed mostly complete, but very weathered from sitting outside. It obviously had not run in about a decade. He said he had bought it just like that, and had never done anything with it other than pour some oil down the spark plug hole. He was an old racer and was into collecting old Japanese bikes. He just happened to have these mid 1980's bikes and a bunch of 1970's Husqvarna parts that he had gotten very cheap. I told him that right now it is the 1970's Husqvarna parts that are worth more money, and he said that he had just been giving them away to people who were into that stuff. I wasn't into the older Husqvarnas, but somehow I ended up buying the bike that he called a 1984 also. It had the smaller 35mm Husqvarna forks on it instead of the 40mm Electrolux forks that were introduced for the 1984 model year. I thought perhaps someone had just swapped the forks. The tank and plastic were missing, so I was not sure exactly what it was. The shocks also were aftermarket parts, so it did not look like much of anything. For just $200 though it was a deal I could not pass up. A total of $950 for three Husqvarnas, even if most of it was just worthless junk.
When I looked more closely at the frame on the 500 I saw that it was indeed a 1985. The disk brake had thrown me off, I thought that was introduced for the 1986 model year. It turns out that the disk brake was actually introduced in 1985, but the more common Enduro models didn't get it until 1986. This was a 1985 Husqvarna 500 XC.
At first I was excited to fix up the 500 and ride it to see what the bigger two stroke motor would be like. When I pulled the top end off though my hopes were quickly dashed. The fact that the bottom end had filled with water from sitting outside with a cracked intake boot and was seized up was in itself not the big problem. The rod bearing was free and seemed to be in good condition. It was just the main bearings that were seized solid. I could have split the cases and replaced the bearings fairly easily, and I was going to do this. When I looked the cylinder over carefully though I became very discouraged with the project. The problem was the ports. The port timing was actually slightly higher than on the 1987 430 WR, which in itself did not look good for the longer 84mm stroke length. Then there was the giant 1/4" diameter hole drilled through the cylinder above the exhaust port. Wow, that looked really bad. Is that a stock port? I don't know, but I began to get the impression that the 500 was junk. They have a reputation for vibrating a lot, and the aluminum motor mounts were nearly twice as thick as on the other two stroke motors. The stock pipe was also missing, what was on the bike was a "Dyno Port" brand aftermarket pipe. The 41mm Mikuni carburetor was also setup very strangely with the same Mikuni 400 main jet as the 38mm Mikuni carburetors on the 400 and 430 two strokes. The 1985 Husqvarna spec sheet calls it a 40mm Mikuni, but it really looks like a huge carburetor. The bore diameter is 41mm, but the slide is a giant 46mm diameter. It looks really huge, and that Mikuni 400 main jet is the stock jet listed on the 1985 Husqvarna spec sheet.
This whole 500 motor just looked like huge problems, and I decided to not even mess with it at this point. I just shelved the motor and stripped the bike down for parts. I was thinking about using the 1985 frame for the Lifan 150 project, but in the end I decided to use the other 1986 250 WR frame instead. I left all the 1985 specific parts with the 1985 frame, and I took just the swing arm, linkage and shock. Why the 1985 500 XC swing arm instead of the 1986 500 CR swing arm that I already had sitting around? Because the 500 XC swing arm has a mount for a kick stand. I really like a kick stand if I can get it, as finding trees to lean a bike against when out riding can get cumbersome very quickly.
The 390 motor that came with the dual shock bike was freshly rebuilt, but it had an aftermarket Wisco piston with no rings on it and the gaskets were missing also. Lots of other parts were missing, including the shift lever, kick starter, carburetor, ignition system, pipe, wheels, brakes, fenders, seat and tank. Pretty much just the motor and frame.
The 390 is a really nice looking little air cooled motor. It is as heavy as the later 400/430/500 water cooled motor, but it is smaller and it looks like it should be lighter. The port timing is lower also, so it is probably a much milder torquer type motor. I am sort of interested in running that 390 two stroke, but I would need a chassis to put it in. It does not go in the 1985 and later Husqvarna two stroke frames with the split down tube. The 390 exhaust exits to the side, so it goes in a single down tube frame. The 390 motor would in fact go in a 1984 through 2004 Husqvarna four stroke chassis. Perhaps someday I'll put the 390 motor in a later four stroke chassis, but at this point I sure can't see taking a 610 four stroke out to put a heavier and less powerful carbureted two stroke in. The bare frame and motor does however look really good hanging on the garage wall.
Amazingly I was able to get the front brakes on both the 1985 and 1986 frames working. They were both full of nasty thick dark brown and black gunk, but the cylinders and seals turned out to be in good condition. Both sight glasses were cracked and leaking from sitting out in the sun, but amazingly water had not gotten into the master cylinders. I coated both plastic sight glasses with cyanoacrylate resin to fix them up and seal them, and that has worked amazingly well. I had previously soaked a piece of cured cyanoacrylate resin in brake fluid for a week to see if it would soften, and it did not. The plastic sight glasses themselves appear to be made of some sort of clear acrylic plastic, so the cyanoacrilate resin tends to be compatible.
The brake on the 1985 chassis bled through fairly easily and started working well once I got the brake fluid to come through clean. The brake on the 1986 chassis was however more stubborn. The piston was seized in the cylinder, so I had to take the cylinder all apart and knock the piston out through the hydraulic fitting end. The cylinder and seal looked to be in good condition, but when I put it back together I still could not get the system to bleed through. I got brake fluid to flow through the caliper and out the bleed screw, but the brake stubbornly remained totally mushy with no "peddle". One problem was that the adjuster on the lever was run all the way in so that the piston was not able to fully retract. The adjuster was frozen solid in the lever and would not turn. I tried replacing the pivot bolt with a smaller bolt so that the lever would fully retract, but the hydraulic system still would not bleed through and function. When this did not work I put the original pivot bolt back in. What I did was to just leave the system full of clean fresh brake fluid, and each day when I walked past I gave the lever a few squeezes. Eventually I started to get some "peddle" at the lever, but it was still mushy and just went all the way down when I squeezed harder. At this point it was again seeming like the piston not fully retracting that was the problem. This time I tried a new technique to get the adjuster freed up, I heated the aluminum lever with a torch. With the lever heated up until the old grease was burning and bubbling out of the threads I was finally able to get the adjuster to turn. Once it started turning it freed up quickly and began to work as new. I had two other 1990's levers that also had frozen adjusters, so I tried the same heating technique on them. One of them I got to free up like the '86 lever, but on the other one I broke the slotted adjuster bolt by torquing on it to severely with a big flat blade bit in a socket.
As soon as I put the lever back on with the adjuster set so that the piston would fully retract the front brake system on the '86 chassis bled through and worked. The feel at the lever on both the '85 and '86 are firm and consistent, the master cylinders appear to be in perfect condition despite all those years of sitting out in the weather with old brake fluid in them. Amazing.
The steering heads on both bikes were somewhat frozen up also, but when I took the 1986 apart I found that the bearings were in sort of OK condition. The lower bearing and race was a bit rusty, but when I cleaned it up and greased it the steering head worked just fine with essentially no noticeable binding or looseness.
One of the sub frame mounting bolts on the 1986 frame broke as soon as I started to give it a turn. It felt like someone had broken that bolt, but then had stopped short as soon as they felt it let loose a bit. It just broke through as soon as I turned it. Drilling out the hard bolt was a bit of a chore, but I was able to get it out using a high quality alloy drill bit. I tried an easy out, but the thread was rusted solid and would not turn. I had to drill it all the way out and then chase the threads with a tap. It was a lot of work, and the threads got a bit damaged but it did turn out well enough. There was plenty of thread in the bung on the frame so damaging some of the outer end of the threads is not really any sort of a problem. The tube welded into the frame does go all the way through also, so even if the threads ended up fully toasted the frame could always be converted to use a through bolt like the 1991 and later Husqvarna frames have.
The swing arm pivot bearings on the 1985 swing arm were in very poor condition. The inner races on the right side were horribly worn, and the rollers were broken up into little pieces. The left side bearings were in fairly good condition, and the left side inner races were not too bad either. It was only the right side that was totally toasted. I didn't have much in the way of bearings to put the swing arm on, but I did manage to find enough inner races to get it together fairly well. Two of the inner races that came out of the 1987 430 WR were in sort of OK condition. For bearings I knocked the drawn cup needle bearings out of the broken 1992 swing arm I had lying around, and amazingly they came right out. The bearings out of the 1992 swing arm are only 12mm wide, but they were still in like new condition so I didn't even need to order new drawn cup bearings.
How did the 1992 swing arm get broken? That's a good question. I came back from riding the 1992 Hsqvarna TE 350 one day and I noticed that one side of th elinkage mount was broken off of the swing arm. How had one side broken without the other side breaking? That seems impossible. I took teh bike out again to see how much it would take to break the one remaining side. At first I rode very slowly and just bounced over some bumps to put a load on the suspension. The one remaining side of the linkage mount did not break. I rode faster and faster to see if the one remaining side of the mount would break, but it did not. After a while I was blasting along like normal with the crappy Showa suspension bottoming hard at both ends, but the one remaining side of the linkage mount didn't break.
I replaced the swing arm with a 1997 swing arm anyway, as I was quite sure that the one remaining side would eventually fatigue and break through. The load on that one remaining side is much higher than half of the normal load. With both sides of the mount in place the load is just pulling straight on the mounts. With one side broken there is also some amount of bending load on the one remaining side of the mount. Bending the aluminum back and forth like that would eventually cause ti to fatigue and fail if the load is anywhere close to the breaking strength of the material.
The linkage off the 1985 chassis was stuck, but it turned out to be in good condition. It just needed to be cleaned and lubed. If it had been run like that without grease in it the bearings would not have lasted long. With the 1985 shock, linkage and swing arm installed the 1986 frame was ready to go. I just needed a motor to put in it.
At first I was not sure which motor to order, the Lifan 140, the Lifan 150 or the YX 160. They all cost about the same $500. The XY 160 was actually a bit more expensive because it did not come with a carburetor, an ignition coil or a CDI control box included in the $450 purchase price. The YX 160 was interesting in that it is even more displacement on nearly the same motor platform. It is a 60mm bore on a 57mm stroke length for a displacement of 161cc, and it uses 8mm cylinder studs spaced out wider to accommodate even larger bore diameters. There are apparently 63mm, 64mm, 65mm and 67mm big bore kits available. The 67mm bore on the 57mm stroke would bring the displacement up to 201cc. The 63mm, 64mm and 65mm sizes are direct bolt on replacements, where the 67mm size requires some machine work on the cases. The XY cylinder head is somewhat modified to take bigger valves for the larger bore diameter. The problem is that the stock YX 160 does not actually come with significantly larger valves. The YX 160 comes with the same 23mm exhaust valve as the Lifan motors and a very slightly larger 28mm intake valve.
Cylinder heads for the XY 160 are available with a 24.5mm exhaust valve, a 30mm intake valve and roller follower rockers, but it is currently $325 for that modified cylinder head. There is also the Zongchen 155 that uses the same wider spacing with 8mm cylinder studs. The Zongchen has a 60mm bore and a 55mm stroke length for a 156cc displacement and has a 23mm exhaust valve and a 28mm intake valve. The cylinders and cylinder heads are interchangeable between these big bore Zongchen and YX engines. So far I have not seen a U.S. based supplier of the Zongshen 155, but the XY 160 is currently in stock in California as are the big bore and big valve parts. Both 64mm and 67mm big bore kits are stocked by quite a few U.S. suppliers at a current price of about $200, it is the motor itself that seems harder to come by. In general the Zongshen 155 and XY 160 parts seem to be much more expensive at this point, and not as widely available. It seems that the reason that the Zongshen and YX big valve cylinder heads and big bore kits are more widely available is that the pistons, cylinders and cylinder heads are interchangeable with parts for the Kawasaki KLX110 and Suzuki DRZ110. Most suppliers of Zongshen 155 motors and parts are in England, France and Germany, but at least one Australian company carries Zongshen 155 motors and a wide selection of parts as well. Zongshen 155 motors and parts seem to be available individually directly from China also, but shipping on a single 50 pound motor tends to be rather expensive. Smaller parts like pistons, carburetors, ignition modules, valves etc. seem to be fairly inexpensive to ship directly from China these days, although it does take longer.
The Lifan 150 on the other hand is available from a number of U.S. suppliers, and the Lifan 150 parts seem to be widely available. The Zongshen 155 and the YX 160 both use the same ignition system as the Lifan 150, and they also have clutch covers that look very similar to the Lifan 150. The Lifan 150 is very much like the Zongshen 155 and YX 160, but it still uses the narrow cylinder stud spacing of the original Honda 50 and Honda 70 air cooled horizontal four stroke motors. I decided not to go for the YX 160 at this point, just because it did not appear to be any better in stock form. Getting the 200cc potential out of the XY 160 requires a number of expensive additional parts, and the valve size still ends up too small. Even with the 30mm intake valve the YX/Zongshen cylinder head looks like it is really for about a 54mm bore, not a 60mm or 67mm bore. The cylinder head might be able to be modified to take even bigger valves, but that is substantially more of a project than just bolting in a complete running motor.
There are also four valve per cylinder options now available from Daytona. The old Daytona 150 two valve engine appears to be nearly identical to the Zongshen 155, but with the very slightly shorter 53mm stroke length for a 150cc displacement. The old Daytona 150 comes stock with the same 28mm intake valve as the Zonshen 155 and the YX 160, and the same 30mm intake valve equipped KLX based cylinder head and big bore kits also fit. There are apparently some exhaust port and exhaust pipe differences between some of these 8mm cylinder stud engines, but as far as the cylinder and cylinder head bolting onto the cases they are interchangeable. Some of them come with what is called the Kawasaki exhaust port, and apparently some of the 8mm stud engines come with what is called the Honda exhaust port. I believe it is the XY 160 that has the Kawasaki exhaust port and the Datona 150 that has the Honda exhaust port, but I am not entirely sure about that. In any case they both use the wider spaced 8mm cylinder studs as opposed to the narrow spaced 6mm cylinder studs of the old Honda motors and the Lifan motors. There are smaller displacement motors from these other companies that also use the narrower 6mm stud spacing, but very confusingly there are also 125 motors that use the wide spaced 8mm cylinder studs.
The new "Anima" Daytona engines are on the same basic platorm, but they use a four valve cylinder head with roller follower rocker arms. With insuficient valve sizes being a widspread and pervasive problem on nearly all of the Honda based horizontal air cooled four strokes the four valve option might seem appealing. There are huge advantages to four valves per cylinder. Smaller valves are lighter, use lighter springs and can use more aggressive camshaft profiles. Two intake valves tend to have a much larger circumfrence than one larger intake valve, and this larger circumfrential length means better flow durring the all critical last part of the intake event when the valves are substantially closing. Big advantages, but not necesarily a good idea for an air cooled engine. The big thing about four valves on an air cooled engine is lack of cooling, and that's not just from making more power. The four valves block off the cylinder head much more substantially than two valves, leaving litte room for heat to escape. Many of the four valve horizontal air cooled engines have very small valves with a narrow valve spacing for smaller bore sizes. This leaves lots of room around the outsides of the valves for big bore engines to cool, but the central part of the cylinder head still ends up substantially blocked off with little means for the inner sides of the exhaust valve seats to cool. The very small valve sizes do limit power output, which reduces chances of overheating at full tilt. If the original goal was to increase power output though the four valve cylinder head then does not accomplish much of anything. There is more performance potential with a four valve cylinder head, but it seems like a mismatch for the cheap little air cooled motors. A correctly sized two valve cylinder head could deliver very good performance also, with better cooling and less chance of overheating at the same power output levels. An air cooled engine can safely make more power with two valves per cylinder than with four valves per cylinder. Air cooled engines are very different than water cooled engines. Water cooled engines run cooling water between the valves to carry heat away, and this makes an absolutely huge difference in a high performance four valve per cylinder engine where the cylinder head is chock full of valves.
The Daytona Anima 4V motors are available in 150 and 190 versions, and they are available from several U.S. based suppliers. The prices are however extremely high at this point, $1200 for the 190 and $1100 for the 150. And that does not include the kick start lever, shift lever or carburetor. Both the 150 and 190 Daytona Anima 4V engines use the same cylinder head and the same 62mm bore diameter, but the 190 is stroked out to 62mm for a 187cc displacement. Big bore kits similar to those used on the Zongshen/YX/Daytona two valve engines are available for similar prices, and even come with pistons with four valve reliefs. A 67mm big bore kit on the 62mm stroke length Daytona 190 is a huge 219cc displacement. Huge considering that it still bolts into an original Honda 50 or Honda 70 chassis from the 1960's. Rated power output for the 187cc version is a modest 23hp at 9,400RPM, but it does carry that full power output all the way up to 11,000RPM with the recomended $180 28mm carburetor. That is screaming for a 62mm stroke length air cooled engine.
The YX 160 is also marketed as the Piranha 160. The YX 160 and the Piranha are not just the same design manufactured by different companies, they appear to actually come from the same factory. The interesting feature currently only available on the Piranha brand motors is eclectic start. Many of the smaller 70, 90 and 110 Lifan centrifical clutch motors have been available with electric start for many years, but the higher performance four speed manual clutch 125, 140 and 150 Lifan motors have not seemed to be available with factory installed electric start. The Piranha 150 electric start appears to be the exact same motor as the two valve Daytona 150, but with a potentially highly desirable electric starter instead of the kick starter. The electric start Piranha 150 is currently in stock with at least one large retailer in California for $600, including the wring harness, ignition coil and CDI control box.
All of these YX, Zongshen, Daytona and Piranah motors are based on the newer cases with the wider spaced 8mm cylinder studs, and they are heavier also. They may share all of the same bottom end and transmission components with the old Honda motors, but the new motors somehow weigh about 10 pounds more even with a two valve cylinder head and kick start. A 10 pound increase in weight is a lot for a sub 40 pound motor.
I was tempted to go for the Lifan 140 because the smaller 55mm bore diameter seemed better matched to the 27mm intake valve and 23mm exhaust valve cylinder head that will actually go on a 52.5mm bore. In the end though there were a number of reasons to go with the Lifan 150. One was the displacement. Since the bottom end is really for 300cc of displacement getting that extra little bit of displacement seemed highly desirable. The big reason to go with the Lifan 150 though was to get the high end ignition system. The 9 degrees of crankshaft rotation of all-at-once advance on the Lifan 125 has been extremely annoying, and the Lifan 140 uses the exact same ignition control module.
I ordered the Lifan 150 motor, and also a "Project Bike" pipe and another "27mm" carburetor. When the "27mm" carburetor showed up it looked very much like the 24mm "27mm" HS Japan PZ27 carburetor I put on the Lifan 125. This "27mm" carburetor was however labeled "HONG DA Designed In", instead of "HS Japan". It is also labeled PZ27, and it has the same "93C" labeled 22mm slide. It looks like the same carburetor, and all the parts appear to be interchangeable. Some of the parts just have a slightly different look and finish to them, like they came from a different factory. The "Hong Da" carburetor came with another unmarked pilot jet, but the main jet is clearly labeled "95".
I suspect that it is the 95 size that is going to be required for both of the Lifan motors, but I had only one of the 95 size jets. I noticed in looking in a catalouge that the main jets in the 24mm "27mm" PZ27 carburetors have all the same external dimensions as Keihin 99101-393 series main jets and that the pilot jets have all the same external dimensions as the Keihin N424-21 series pilot jets. I ordered a 95, a 98 and a 100 to cover all the bases. I also ordered a 42 pilot jet and a 45 pilot jet.
When I looked over the new Lifan 150 motor the first thing I noticed was that I was able to see the table through the open intake and exhaust valves at split overlap. Wow, this camshaft has a lot of overlap. It was not just a little sliver of light I could see through the open valves, no I could actually see the table down there through the combustion chamber.
When I measured the camshaft duration I got about 250 degrees at 1mm valve lift. A much bigger camshaft than came in the Lifan 125. When I measured the intake and exhaust opening and closing times at 1mm valve lift I found that it is a very strange camshaft. It might have lots of duration, but it also has an extremely narrow lobe separation angle, just 100 degrees. The camshaft is also installed five degrees advanced, so the intake valve closing time is really very early. About the same intake valve closing time as on the Lifan 125. Exactly the same intake valve closing time to 1mm valve lift as near as I can tell from my rough estimates. A very strange camshaft indeed. The Lifan 150 camshaft also has more lift than the Lifan 125 camshaft. The Lifan 150 has 0.28" of valve lift on both the intake and exhaust, where the Lifan 125 camshaft lifts the valves hardly more than 0.20". Lifting the 27mm intake valve 0.28" is like a 2.02" intake valve on a small block Chevy lifting 0.530". That is quite a bit of lift. And the Lifan 150 holds that maximum lift for quite a bit of duration also, 34 degrees of crankshaft rotation at the full 0.28" valve lift. The all critical intake valve closing ramp is fairly aggressive, although more aggressive intake valve closing ramps are sometimes used. The Lifan 150 camshaft closes the intake valve from 5mm valve lift to 2mm valve lift over just 40 degrees of crankshaft rotation.
When I turned the Lifan 150 motor over in first and fourth gears and counted the number of revolutions required to turn the front sprocket one revolution I found the same 3.70:1 primary reduction ratio as on the Lifan 125. With the considerably lower 3.182:1 first gear versus the 2.833:1 first gear on the Lifan 125 it takes a 17 tooth front sprocket to have the same first gear ratio as the Lifan 125 with a 15 tooth front sprocket. The Lifan 150 comes with a 428 15 tooth front sprocket, and I had ordered a 16 tooth also. When I found that the primary reduction is the same as on the Lifan 125 I had to order a 17 tooth front sprocket.
For the Lifan 125 with a 15 tooth front sprocket in the 1986 Husqvarna chassis with an XL185 rear wheel and the stock 50 tooth rear sprocket I was just able to squeeze it together with the longest 134 link 428 chain. Using all 134 links the rear axle came out all the way forward, but that's perfect for the little air cooled 125 four stroke that can never hope to make more than about 1/4 the power of the 400 two stroke. For the Lifan 150 with a 17 tooth sprocket I had to order two 102 link 428 chains. Interestingly though the total price was $20 either way. Somehow getting those extra few links really jacks up the price of a 428 chain.
The clutch cover on the Lifan 150 really is a whole lot different than the clutch cover on the Lifan 125. The first thing that can be seen is that the clutch is on the other side of the primary reduction. On the Lifan 125 and Lifan 140 the clutch is rather strangely located on the end of the crankshaft. On the Lifan 150 the clutch is in it's usual location on the transmission main shaft. What this means is that the clutch on the Lifan 125 spins nearly four times as fast as the clutch on the Lifan 150. Spinning the clutch faster increases it's capacity in terms of the static coefficient of friction, but spinning the clutch faster does not increase it's thermal capacity. What spinning the clutch faster also does is throw a lot more oil around, which wastes more power and reduces overall efficiency. Especially under light to medium loads that extra drag of a faster spinning clutch is rather significant.
The other significant difference is that the Lifan 150 is a lot narrower, more than an inch narrower. The total width of the Lifan 150 is just 9-5/8 inches.
The first challenge with actually installing the Lifan 150 motor was to build another set of mounting plates. I had toyed with the idea of cutting one of the down tubes off of the '86 250 two stroke chassis to make room for the motor to lay down fully horizontal. This seemed like a reasonable idea. Having the Lifan 125 Husqvarna to look at I could see that the right hand side of the cylinder head would clear the right hand side downtube. It is just the left hand side with the timing cover that sticks out. Cutting just the left hand side downtube off would make room for the engine to lay all the way down horizontally, and there would still be the right hand side downtube to hold the bottom of the frame in place. Without bolting the motor into the front part of the frame the chassis is already somewhat weakened from the stock configuration, but that giant 56mm main tube is very substantial. The Husqvarna chassis obviously would work without any downtube or lower frame whatsoever. The lower part of the frame is however a very nice skid plate, so I was not inclined to remove it entirely. Removing the lower part of the frame would also raise problems with the foot pegs. Honda/Lifan horizontal motor powered bikes normally use foot pegs mounted to the bottom of the engine cases, but these stock foot pegs would not work on the Lifan Husqvarna as the engine is farther forward. A custom foot peg mount could be built, but the weight savings over the stock Husqvarna frame might not be all that substantial. It is a really nice skid plate, and it is already on there.
In the end I decided to mount the Lifan 150 in exactly the same location and orientation as we had mounted the Lifan 125 several months earlier. Since the 40 pound Lifan motor is considerably lighter than any of the stock Husqvarna motors it did not seem like a bad thing to tilt it up somewhat. Keeping the mass low is generally good, but keeping the mass towards the center of the bike is also good. When a bike is extremely excessively heavy the most important thing tends to be keeping the mass low so that the bike does not have so much of a tendency to just fall over. With the weight of the 1986 Husqvarna being substantially reduced with a lighter motor and the removal of the radiators, shrouds, hoses, air box ext. the tilted up engine installation seems perfect.
When we were building the Lifan 125 my father kept saying that we should take the pattern off of the final motor mounts so we would have it for later, but the day that I did the final adjustment and mounting I just put it together without tracing the final shape. In building the Lifan 150 mounts I was faced with the dilemma as to whether or not to take the Lifan 125 motor out to trace one of the mounting plates. Tracing the mounting plate would be a quick and easy way to get the project going, but somehow I just did not feel like taking a running bike apart simply to copy parts.
What I ended up doing was just measuring between all of the mounting bolts to layout a new plate pattern. This was a bit harder than might be expected. Measuring between the upper motor mount and the upper frame mount was easy, as both bolts were well accessible and the heads are on the same plane. The bolt heads both rest directly on the mounting plate. For the lower motor mount and the swing arm pivot bolt the measurements were much more difficult. The swing arm bolt is well accessible, but it's end lies on a much different plane than the mounting plate.
The solution was a combination of trigonometry and creative measuring. By measuring both the straight line distance from the swing arm pivot bolt head (nuts on both sides actually) out to the bolt heads on the two accessible mounting bolts as well as the offset of the swing arm pivot bolt head from the mounting plate I was able to readily calculate the location of the swing arm mounting bolt on the mounting plate. Whew!
The complication with the lower engine mounting bolt is that it is tucked up inside the chassis without much access. Finding the location of the lower motor mount involved two measurements. I was able to easily get the distance between the two motor mounts by measuring the Lifan 150 I had sitting on the kitchen table, but I still needed a measurement from that lower motor mount out to the swing arm pivot. This I was able to get by measuring from the lower motor mount bolt head out to the spacer on the swing arm pivot bolt.
These spacers were an interesting bit of the Lifan 125 installation. I kept saying that they would be fine made out of 1/2" schedule 40 gas pipe, but my father kept insisting that he wanted the spacers to fit precisely on the 14mm swing arm pivot bolt. The 1/2" schedule 40 pipe with it's 0.622" inside diameter would leave a substantial 0.035" on each side of the 14mm bolt, or more likely the full 0.070" on just one side. This seemed just fine structurally, but for some aesthetic reason my father insisted on turning the spacers out of pieces of schedule 80 pipe. It took him hours to get the lathe setup to turn the inside diameter out using a long boring tool, but he did get a precise fit of the spacers to the 14mm pivot bolt.
When I was trying to make the measurements for the new Lifan 150 mounting plates I finally found a use for the precise fitting spacers. They meant I could just measure to the spacer without any additional steps. If it had been a piece of schedule 40 pipe I would have had to loosen the swing arm pivot bolt and push the spacer over to one side to be sure of where I was measuring to.
Once I had all of the measurements written down, the trigonometry worked out, and was laying the plate out on a piece of paper I realized that something was wrong with my dial caliper. I was using the dial caliper to layout the drawing on the paper, as it is faster to use than a scale. What I noticed sitting at the comfort of my desk was that the dial was off by 0.050". The dial caliper had been dropped on the concrete floor earlier in the day, and I had to file a ding off of the tip of one of the jaws. What I had not noticed in the haste of shop work was that the dial caliper had skipped a tooth and was off by exactly 0.050".
With the dial caliper reset to read correctly I had to go back over all of my measurements, most of which I found to be off by 0.050". Amazingly though some of the measurements were correct, and some were even off by 0.100". Dial calipers are fast, accurate and convenient, but they do have to be zeroed to work!
With the correct measurements worked out again I got the four holes laid out on a piece of paper, and then I did the layout again on a piece of sheet steel. We had only little scraps of the 0.135" plate left that my father had used to build the mounts for the Lifan 125 Husqvarna, so I just used some rusty old 0.10" plate that we had lying around. It was a big piece of 0.10" plate that I had bought many years ago, and it has long been my favorite material to build mild steel parts out of. I can even cut the 0.10" plate with large hand shears, which is sometimes very convenient.
For this project I laid out the piece, and drew the aproximate outside shape with chalk. I made up the shape of the plate where it goes around the engine cases the same way that my father had on the Lifan 125 project, by making a series of cardboard templates. Again working inside at the kitchen table making these templates was quick and easy. As the 0.10" plate is thinner than what we used on the Lifan 125, and the Lifan 150 is more displacement with a longer stroke length, I drew the pattern with more material around the mounting bolts, particularly leaving a generous amount of material sticking out behind the lower motor mount and the swing arm pivot bolt.
My father cut the rough shape out with hand grinders, and painted the pieces. Again the task of drilling the holes and fitting the final shape to the bike and the frame was my domain. The important part of these mounting plates is the skinny 1.1 inch part between the Husqvarna frame and the engine cases. This connection between the lower part of the plate and the upper part of the plate is necessary to hold the engine and keep the two parts of the plates from rotation relative to each other. With the thinner 0.10" plate I was thinking that I might want to weld a reinforcing bar across that thin part of the plate. Adding a reinforcement would also allow this part of the mount to be skinnier so the motor could be moved back even farther. I had left a generous 7/16" of space between the back of the 15 tooth 428 sprocket and the Husqvarna swing arm on the Lifan 125 Husqvarna, and I had been thinking that this could be closed up somewhat to move the motor back and allow it to tilt down farther.
For the Lifan 150 though the 17 tooth sprocket would take up nearly half of this space, so there actually ended up being little reason to try to mount the motor back farther. I decided to just go with the plane 0.10" mounting plates with no welding. They will probably be strong enough. I left the plate as wide as possible above and below the narrow 1.1" pinch of point, so the skinny part of the plates are only in shear and don't experience much in the way of any bending moment. I remember an old professor once saying that shear and bending moment analysis is the single most useful analytical technique from all of advanced structural design theory, and this certainly has seemed to be true over the decades. Part of why shear and bending moment analysis is so useful is that it is rather intuitive and easy to apply. I rarely seem to be able to remember most of what went blurring past in all of those engineering classes, and I have a strong aversion to digging through text books to look up forgotten lessons. Shear and bending moment analysis though seems to have an inherent sticktuitivness. I always seem to be able to derive the formulas for shear and bending moment analysis from scratch, no matter how many years it has been since the last time I thought about it. The basic idea is that the shear stress and bending stress are additive. This is an oversimplification, but it does work. The reality is that the outside part of a structural member is stressed much more severely than the middle or inner parts from a bending force. This is complicated for a variety of reasons, and analysis gets into not only difficult to solve integrals but also has a great deal to do with variations in structural properties of a materials. Mathematically shear and bending moment analysis is simple and very useful, and why this is true is even more complex than the integrals required to do a full load analysis on part of an odd shapped structural member. The reason that shear and bending moment analysis is so easy to use is that it is partially build into us. Tens of thousands of years of building tools and weapons out of pieces of wood and bone have selected for an ability to predict when something will break. How we do this is with shear and bending moment analysis. Identify the material, look for clues about variations in structural properties, look for knots, cracks, dents or other blemishes or discolorations that would indicate a weak spot, build a three dimensional model of the profile of the piece, determine how the piece is loaded at each end and if there are any significant intermediate loads and then calculate the shear and bending loads along the length by working back and forth visually. People who have never heard of calculus can sometimes do this, although understanding what you are doing and why makes it much easier.
The simplest and most effective way to apply shear and bending moment analysis mathematically is to arbitrarily pick a portion of the outer part of a member as the tensile carrying zone. This is not something that the old professor I so fondly remember told us to do. Rather it is a simplification of a full structural analysis using the actual shape of the part. Just arbitrarily picking a portion of the material as the tensile zone provides something solid to work with. The tensile stress is the bending moment divided into the product of the cross sectional area of this arbitrary tensile zone multiplied by the lever arm from an arbitrarily chosen pivot point located somewhat into the material from the surface at the inside of the bending load. Divide the load by the product of the area multiplied by the lever arm, that is the tensile stress on the material. Then this tensile stress is added to the shear stress, that is what shear and bending moment analysis is really about. To find the shear stress on that tensile zone the total shear load is divided by the total cross sectional area at the point of analysis. For more on shear and bending loading of structural members see Structural Analysis.
This form of structural analysis is something that I don't use much with Husqvarnas, but it was very useful in building a sailboat trailer and also in rigging the sailboat. It allowed me to satisfy myself that the existing boom would not break if I mid boom sheeted it, and it also allowed me to build a lightweight trailer tongue extension to ramp launch the boat at rather shallow angle boat ramps. My first mild steel tongue extension actually did "creep" into a bent shape over the course of the first few times we used it, and I had to weld reinforcing plates on top and bottom to keep it from bending farther. The sizing of these reinforcing plates was greatly simplified by using shear and bending moment analysis.
Dirt bikes don't tend to be so predictably loaded though. Things break in crashes, or close call near crashes where bumps are bounced over in very unusual ways. If everything were designed to take only the loads of smoothly riding a freshly groomed motocross track then a crash would absolutely scatter the bike with tons of broken parts all over the place. Beefing parts up just by designing for the same loads of increased magnitude results in an extremely heavy bike. Structural design is still very useful in building cheap and light dirt bike parts that don't break, but it is complicated. Engine vibration is a big deal. Loads from vibration are in addition to other loads not instead of other loads.
When it comes to motor mounting plates the single most likely failure mode is eventual cracking near the mounting bolts due to vibration. If the material in that area is also heavily stressed from just from the weight of the motor then the vibration causes failure much sooner. That's not just the static weight of the motor, but the weight of the motor as the suspension is compressing. And the suspension sometimes ends up rapidly compressing quite a significant portion of run time on a dirt bike.
For a one off custom bike the motor mounts typically are designed and built before the vibration characteristics of the engine are even seen. I hope that the Lifan 150 won't have that extreme vibration right at 6,000RPM that the Lifan 125 does, but that is something that I don't yet know while building the motor mounts. All I can do is guess and hope for the best. Making a reasonable guess though does keep weights down considerably. The new 0.10" thick motor mounts for the Lifan 150 are somewhat lighter than the 0.135" thick motor mounts on the Lifan 125 despite the more generous sizes around the mounting bolts. I suspect that both sets of motor mounts will be sufficiently oversized as to never give the slightest bit of trouble.
Building with structural carbon steel plate instead of soft mild steel sheet would be the single easiest thing to do to reduce weight. Instead of 300g each for the mild steel mounts, structural carbon steel mounts could be about 200g each with no danger of vibration failure thousands of hours of run time later. Fabricated mounts with flanges on them could be even lighter, and of course carefully designed CNC machined aluminum mounts could also be very light.
After the 0.10" mounting plates were cut out I remembered that I had actually wanted to mount the Lifan 150 somewhat lower in the chassis that the Lifan 125 was mounted. The main reason to mount the Lifan 150 lower was that it would be taking a 17 tooth front sprocket versus the 15 tooth front sprocket on the Lifan 125 Husqvarna. The 17 tooth sprocket sticks up 0.16" higher than the 15 tooth sprocket, so would tend to work best with a 0.16" lower engine mounting location. When I looked at the way the chain fits on the Lifan 125 I realized that the chain was actually too far above the top of the swing arm. With the rear suspension extended the chain just touched the top of the 0.10" thick polyethylene chain slider on top of the swing arm. When I sat on the bike though the chain was a whopping 0.34" above the top of the swing arm. It seemed like the Lifan 150 should be mounted considerably lower.
As I had left quite a bit of extra material around the mounting locations on the 0.10" mild steel plates I did have room to move the motor down somewhat. I scribed a line between the center punch marks I had made for the swing arm pivot bolt hole and the upper mounting bolt hole, and I measured up this line 0.30" from the two center punch marks. I made new punch marks at these 0.30" higher locations and drilled the left hand plate.
When I test fit the plate on the frame the bolts went right in, a perfect fit on the first try. What I also noticed though was that there was about 0.20" of extra clearance between the plate and the frame. I double checked my original layout, and sure enough somehow the plates had gotten cut back 0.20" farther than I had marked. The plates looked good though, and I suspected there would still be enough material between the engine and the frame to do the job. I also moved the engine down about 0.08" bellow where I had originally marked on the plates, so the Lifan 150 ends up a total of nearly 0.40" lower than the Lifan 125 Husqvarna.
With the plates completed and painted black the last step of the installation was to cut the spacers for the swing arm pivot bolt. This I did with a pipe cutter using 1/2" schedule 40 gas pipe, and I filed the burrs off the ends. In my excitement to get the engine mounted I had however forgotten to account for the difference in plate thickness, and I had made the spacers the same length as on the Lifan 125 Husqvarna. Instead of cutting new spacers I just added a 0.065" thick washer between the plates. The washer was a bit difficult to force in, but I got it together and the swing arm pivot bolt tightened down nicely.
With all the bolts torqued down the Lifan 150 sat nicely in the frame. It looked just like the Lifan 125 Husqvarna, but sitting about 3/8" lower. It also looked like the Lifan 150 was not tilted up quite as much as the Lifan 125, although the difference seemed very small.
As soon as I got the swing arm pivot bolt torqued down though I realized that the left side swing arm pivot bearing was very loose. That left side bearing had looked fairly good, so I had only replaced the completely toasted right side bearing. I still had that other bearing in the broken 1992 swing arm, so I pulled the swing arm off of the Lifan 150 Husqvarna again.
The swing arm pivot bolt spacers and washers fit tightly enough that I was able to pull the swing arm pivot bolt out and everything just stayed in place with the motor hanging from the torqued down upper mounting bolts. I beat the good bearings out of the 1992 swing arm, and the worn bearings out of the left side of the 1985 swing arm and then I beat the 1992 bearings into the 1985 swing arm. With the swing arm back in place and the swing arm pivot bolt torqued down again the swing arm moved freely but had no noticeably side to side play. Perfect.
FOr a rear wheel I bought another 1979 Honda XL185S rear wheel, and this one turned out to have less rust on the inside of the rim. Instead of grinding material off of the 1985 swing arm to get that extra little bit of clearance I instead turnd the 50 tooth sprocket around. There is a pocket cut on what was originally the right hand side of the 50 tooth Honda sprocket, so turning the sprocket around moves it in towards the center of the bike. The pocket was however not quite big enough to fully accept the flang nuts, so the nuts sit tilted in towards the center of the wheel. This looks really bad, but it actually does something usefull. It pushes out on the rubber sprocket mounts and jamms them tight. Those Honda rubber mounts had been seeming to actually cause some chain vibration on the Lifan 125 Husqvarna sometimes at certain rather slow bike speeds and very low engine speeds, so jamming them solid seemed like an excelent idea.
When I put the rear wheel and chain on I got a few surprises. The first was that I actually only needed 134 links of chain. At first I thought there might be something wrong with the chain, but when I pulled it tight and measured 20 links it was exactly 10 inches within 1/64". The 134 link chain was just able to go on the 17/50 sprockets with the rear axle adjuster bolts all the way in as far as they would go. It turns out that the stock adjuster bolts on the 1985 swing arm allow a slightly shorter wheelbase than the stock adjuster bolts on the 1986 swing arm, so even with the 17 tooth front sprocket the 134 link chain just about fit.
The next big surprise I got was that the chain seemed to be loosening up more when the rear suspension fully extended than it does on the Lifan 125 Husqvarna. This surprised me, as I had somehow been expecting the opposite.
The problem is that the 1985 through 1986 linkage is offset to the left side of the bike, so installing a left side drive engine requires that the chain be routed bellow part of the linkage. On the Lifan 125 I had accomplished this by mounting a chain roller on a plate bolted to the linkage pivot bolt. With the chain roller just behind the linkage, and adjusted so that the chain just avoids the linkage, the chain drive works fairly well. The roller keeps the chain from rubbing on the linkage, and the roller location somewhat behind the linkage minimizes loosening of the chain as the suspension extends. In fact the chain tension remains remarkably constant on the Lifan 125, with the chain just loosening slightly as the swing arm is either compressed or extended from the normal ride height.
The Lifan 150 installation was however not looking so good. The chain loosened dramatically with the rear suspension fully extended. As it turns out mounting the engine lower to get the top part of the chain to come out just right on the top of the swing arm actually makes the protruding shock linkage a worse problem. At first I thought the larger front sprocket mounted lower would more easily clear the low hanging shock linkage. This seemed reasonable, but the reality is somewhat different. With the center of the front sprocket bellow the swing arm pivot the chain continues to tighten as the swing arm moves up past level, and this means that the chain has to be adjusted looser so that it does not get too tight as the rear suspension compresses. With the chain somewhat loose with the swing arm straight across the loosening of the chain as the suspension fully extends is a very severe problem.
To address the loosening chain when the rear suspension extended I mounted a roller on the frame just behind the front sprocket to hold the bottom part of the chain up. This caused the chain to loop up over this roller when the rear suspension was fully extended, but then with the swing arm straight across with me sitting on the bike the chain just barely touched the top of the roller. As the rear suspension compressed further the chain did not touch this front roller at all. The result is that the front roller takes up a considerable amount of the slack when the swing arm is fully extended. Having to route the chain under the linkage is still a problem, but at least the chain system can be made to sort of work. What it comes down to is that the location of the front sprocket is just fine. The front roller under the bottom of the chain mostly counters any normal problems that would crop up with the sprocket somewhat lower than the swing arm pivot. The problem that remains is that the linkage is in the way, and routing the chain under the linkage is problematic. Perhaps someday I'll swap out the entire swing arm, linkage and shock for parts off of a 1987 Husqvarna. For now though the chain system looks to at least sort of work. The chain is tightest with the suspension compressed 7.5 inches, and as the rear wheel goes up past 8 inches the chain does loosen again.
With a lot of work left to do, including shortening the shift lever, building the custom rear brake lever, building a custom clutch cable housing mount and building the exhaust system, I decided to fire the Lifan 150 up. But first I had to mount and setup the carburetor.
For an air filter I had picked up another Uni cylindrical foam filter, but it was not the same one. The 4" Uni filters that had been in stock in a local store were gone, and in their place was a similar looking filter with no dimensions listed on the tag. It was just listed as being for 1980's Honda ATC110/185/200 or Honda TRX125/200 ATVs. The price was also higher, but it was a somewhat longer filter and it looked like a higher performance design with a larger inside diameter made out of the normal Uni yellow medium cell count foam instead of that gray fine cell count foam on the 4" Uni filter. Being busy with other things in town I grabbed the Uni NU4068ST and paid the $27.
When I got home and opened the package I found that the flange was actually a larger 2" diameter, and it had a strange hard black plastic insert. Looking at the filter through the plastic bag it had been in I mistook that plastic insert for a smaller diameter rubber flange of about 1-1/2". Nope, the plastic insert sure did measure exactly 1.50" in diameter, but it was very hard and entirely useless for adapting to a smaller carburetor flange. The only purpose that insert seems to serve is to fool an unsuspecting buyer who quickly grabs one off the shelf without looking carefully. With the plastic insert removed it was a two inch rubber mount instead of the 1-7/8" rubber mount on the 4" Uni. The 1-7/8" rubber mount very easily squished down onto the 40mm (1.57") carburetor flange, but the 2" mount wouldn't even come close to working. Not only is the 2" mount for a slightly larger maximum carburetor flange diameter, but the rubber is also thinner and shorter. On top of all of that the external bead holding the clamp was a lot smaller on the 2" rubber flange. This all adds up to a dramatic inability to squish down to smaller diameters. All was not lost though, I just cut a short piece of 1-3/4" radiator hose and stretched it over the 40mm flange on the carburetor. Because the inside diameter of the hose was only about 1.3 inches it fit very tightly over the 40mm flange and stayed in place perfectly. The 2" flange on the Uni NU4068ST filter then very easily clamped down on the outside of the radiator hose. A perfect installation, even better than the 1-7/8" mount on the 4" Uni filter clamping directly on the 40mm flange. The longer 5" filter squished a bit up against the frame, but it looked good once installed. It is about the biggest filter that will fit the available space with the Lifan 150 tilted up in the un-cut 1986 Husqvarna frame.
Once again the 24mm "27mm" HongDa PZ27 carburetor went right on the 1986 Husqvarna throttle cable with no modification. I set the needle clip on the HD27B needle in the same second position where I had been running the PZ27 needle in the 24mm "27mm" HS Japan PZ27 carburetor. I installed a Keihin 99101-393 series main jet labeled 95 and a Keihin N424-21 series pilot jet labeled 42. And again I soldered a brass pilot jet extension on so that it would not lift out of the gasoline in the carburetor bowel.
The Lifan 150 fired right up, but it kept stalling after about a half second of run time. It continued to restart easily, and after four or so attempts it continued to run with a stable idle. When I rode off I found very weak torque with stumbling at low engine speeds, and then it just took off all of a sudden and made big power. Wow, really lots of power! About 50% more than the Lifan 125 it seemed. I mean just really big torque. But the torque was also very narrow. It seemed to be hitting at about 6,000RPM and pulled for a short while and then it just ended with some cutting out and stumbling. It seemed like there might be a rev limiter in the CDI control unit, it was just ending so abruptly at all throttle openings when cold or once fully warmed up. I put a timing light on the engine and I found the problem. The advance curve continued to advance up to very high engine speeds. The low idle spark timing was close to 9 degrees BTDC, and then it jumped all-at-once up to 14 degrees BTDC just above low idle. Then it was a smooth advance curve that just kept advancing up to unbelievably high engine speeds. I did not have a tachometer on the engine, but I had to twist the throttle quite far until the engine was screaming at about 6,000RPM before it stopped advancing and leveled off at 25 degrees BTDC. Wow, that is not going to work on a 150cc engine! I complained to the company I ordered the complete motor from, but they initially had nothing to say.
The main jets I had ordered seemed wrong. The 100 appeared to actually have a 0.98mm hole in it and the 98 was even smaller. The only thing I had in that size to measure with was the 0.0388" diameter #60 drill, which isn't a #60 drill at all even though it came in a #60 to #1 drill index. A #60 drill should be 0.40" in diameter, and a 0.039" drill is a #61. In any case the 0.0388" drill stock end would just barely start into the Keihin 99101-393 series size 100 jets, but stuck before going in more than about 1/16". Clearly these were smaller jets. When I carefully measured the tip part of the drill stock that was going into the Keihin 99101-393 series 100 size jets I found that it was in fact a small bit smaller at 0.0386". These really looked like 98 size jets, and the 98 size jets were obviously even smaller.
To sort out the problems I ordered a #80 to #61 drill set and a few loose #63 and #62 drills. I ordered the set and one each of the #63 and #62 drills from one company, and I also ordered just a single #63 and a single #62 from another company. I wanted to make sure that I actually had several #63 and several #62 drills when it was all said and done.
When the drills showed up I had three #64 drills and just one #63 drill. The loose drills from the company that I had ordered the 80 to 61 index from were correct, measuring 0.0368" and 0.0377", but the index had two #64 drills at 0.0355" and 0.0357" and no #63 drill. The other company had sent a #62 drill that measured 0.0378" and a #64 drill that measured 0.0358". Both companies that had supplied #64 drills instead of #63 drills quickly agreed to mail out replacements at no charge, but it was a very frustrating process. In any case I did have enough drills to measure the 95, 98 and 100 Keihin 99101-393 series main jets I had.
The 0.0377" #63 drill stock dropped cleanly through the Keihin 99101-393 series jet labeled 98, but with no side to side wiggle. The 0.0382" diameter 1/16" from the drill stock end of the 0.0384" diameter #61 drill in the cheap 80 to 61 index just started into the Keihin 99101-393 series 98 labeled jet, but would not go in even close to the 0.0384" diameter. Clearly this was a 0.965 to 0.970mm hole and not a 0.98mm hole.
When I measured the Keihin 99101-393 series 95 labeled jet I had been running in the 24mm "27mm" HongDa PZ27 carburetor on the Lifan 150 the difference was even more dramatic. The 0.0367" end of the #63 drill stock went easily into the Keihin 99101-393 series 95 labeled main jet, but the 0.0368" shank would not go in. Clearly this was a 0.93mm hole and not a 0.95mm hole. It is a 93 main jet that is clearly stamped "95". Very confusing and infuriating.
The little drills I ordered seemed very uniform, with no discernable out of round and no discernable taper on the shanks, other than those small 0.0001 to 0.0003" smaller diameters within about 1/16" of the drill stock end. I used a 0-1 micrometer with divisions at 0.0005" which is labeled as a 0.0001" instrument. Normally it is considered that a micrometer with 0.001" divisions is good down to 0.0002", dividing by fifths being all that the trained human eye is expected to be capable of. It is actually possible to get down to 0.0001" with a standard micrometer with divisions at 0.001", but not necessarily reliably. Dividing by 10 visually is somewhat difficult. With the divisions at 0.0005" it is much easier to read the micrometer down to 0.0001", but the accuracy of the measurements may still be only 0.0002" if temperature and pressure are not carefully accounted for (tool pressure not atmospheric pressure). Equalizing the temperatures of all the parts before measuring takes care of temperature differences, and sticking close to room temperature around 60 to 80 degrees Fahrenheit yields the best results. Small drills and jets don't expand much with temperature, but the micrometer itself may be less than perfectly temperature stable. It is just made out of steel that gets bigger when it heats up. Down at very small measurements though the micrometer would be expected to do pretty well even over a range of temperatures, but sticking to close to room temperature is the best way to get actuate measurements down to one ten thousandth. When measuring three and four inch cylinder bores it is quite common to see 0.0003" variations in measurements with the temperature swings from noon to night or when instruments are taken from a heated house to a freezing cold shop to measure a bore. With parts only 1mm across temperature variations tend to be a whole lot less significant when measuring to within a ten thousandth of an inch.
In any case I am quite confident that the 0-1 micrometer very easily gets down to within 0.0002", that is the measurements taken by different operators at different times but under similar temperature conditions would easily be within 0.0002" of each other. The reality is that it seems pretty easy to get down to within 0.0001", and I am pretty sure that I know the sizes of those drills to the nearest ten thousandth. The Keihin 99101-393 series main jet labeled 95 clearly is a 93 size main jet. There seems to be no doubt about that. When I initially complained about the jets seeming to be the wrong sizes the company I ordered them from sent me out duplicates of the Keihin 99101-393 series size 95, 98 and 100 jets. These were exactly the same. After I got the small drills and made accurate measurements I complained that I had ordered a 95 main jet and still didn't have one, but the best the retailer could do was offer me a gift certificate to cover the cost of the jets that had not worked. The jets worked fine, they just weren't the sizes they were labeled.
I put the size 97 Keihin 99101-393 series 98 labeled jet in the 24mm "27mm" HongDa PZ27 carburetor and rode the Lifan 150 Husqvarna around some more. The stumbling was even worse at lower engine speeds, and the peak power seemed a bit lower. The engine was also harder to start. The stumbling at the top of the power band was however gone. The power still seemed to end abruptly much sooner than it should, but it was consistently pulling up there without cutting out or stumbling.
On the first day I had rode the Lifan 150 Husqvarna it was pulling consistently and fairly strongly way down low at the bottom around 2,000 to 2,500RPM, but then it was stumbling and very weak over a wide range of lower and midrange engine speeds before taking off all of a sudden and making big power. With the 97 size 98 labeled main jet and all the other settings the same the smooth and consistent torque down at the bottom was gone, and it was just stumbling all the way through. The stumbling was also worse all the way up to where the engine took off and made power around 6,000RPM. That was all with old gasoline that had been sitting around unattended in a sealed container for several weeks.
I then went to town and picked up 3.5 gallons of fresh 87 (RON+MON)/2 octane rating regular gasoline. I came straight home with no stops, drained the remaining gasoline out of the tank on the Lifan 150 Husqvarna and added a gallon of the fresh gasoline. When I first fired the engine up and rode off there was still stumbling across a wide range of lower and midrange engine speeds, but this went away once the engine warmed up. Wow, no stumbling! Amazing! The power seemed better at 6,000 to 8,000RPM also, perhaps back to where it had been on that first day and there was still no stumbling or cutting out up at the top. The torque was better across the midrange, but still seemed extremely weak. Like considerably less torque at 3,500 to 5,000RPM than the Lifan 125 does. The simple fact that the Lifan 150 was actually running without stumbling though was amazing. It meant the bike was ridable, although the power still seemed way too narrow. The huge jump from first to second was a huge problem, and the engine actually couldn't even get between second and third in the power either. With each shift the power dropped off extremely dramatically, and then only after considerable slow acceleration did it take off and pull again. Pretty disappointing.
I took a hand held chart plotter out in my left hand to see what sort of engine speeds the Lifan 150 was twisting. It turned out that it was able to very easily hit 37mph in second gear, which with the 17/50 gearing is 8,9000RPM. There was no cutting out or stumbling up there, but the power was seeming very flat and perhaps even dropping off a bit around 35 to 37mph in second gear. In second gear there was stumbling and extreme weakness bellow 14mph, and then the engine took off and ran smooth at 14mph and above. This 14mph in second gear is 3,400RPM. In third gear the power was hitting hard at around 39 to 40mph, which is 6,800 to 7,000RPM. In third gear it would pull all the way down to around 25mph, but torque was seeming extremely weak down there. The engine was smooth, but just very weak in the midrange engine speeds. Weaker than the Lifan 125 at the same engine speeds.
The next day I rode the Lifan 150 Husqvarna around some more, and again it was running without stumbling once warmed up. It seemed that the gasoline had remained mostly the same overnight this time, also amazing.
The first task was to build an exhaust system. I had been riding around with big hard plastic acoustic foam lined ear protection instead of a helmet, and I suspected that other people might be getting tired of hearing the poorly running and extremely loud motor go tearing up and down the private dirt road. I wanted to build the new exhaust system all in one day, so that I would know that it was the same gasoline before and after. I had picked up a length of 1-1/4" mild steel tubing, but I was not yet sure exactly what sort of an exhaust system I would be able to build.
On the Lifan 125 I had run the 1" mild steel tubing all the way up to the first U-bend on the "project bike" pipe, and this had seemed to work well. The 0.065" wall thickness 1" tubing had seemed big enough for the 125, but I was worried it might be a bit on the small side for the 150. I couldn't find any 1-1/8" tubing locally, so I had to settle for 1-1/4". The "project bike" pipes that I started with on both of the Lifan motors are made out of 1-1/8" O.D. and 0.055" wall thickness steel tubing that is somewhat harder. It is dimensionally the same size as 1" copper pipe, and I had considered building part of the exhaust system out of copper. A 10' length of 1" copper was however twice as expensive as a full 20' length of 1-1/4" mild steel tubing, and I was not thrilled about building a copper exhaust system that would probably fail from vibration in a rather short period of time.
On the Lifan 125 Husqvarna we had to go all the way up to the front U-bend to get the low hanging 3.2 gallon Enduro tank to clear the exhaust system. On the Lifan 150 Husqvarna though with the motor mounted lower the tank did clear the "project bike" pipe, although not by enough really. I had considered starting towards the back of the "project bike" pipe and just connecting up to the Husqvarna muffler as my father had done on his first attempt of an exhaust system for the Lifan 125 Husqvarna. What decided it was how I was able to bend the 1-1/4" tubing. Being only slightly smaller on the outside than 1" steel pipe I was able to use the hydraulic jack based pipe bender to get some bends. The 0.065" wall tubing was supported well enough by the fitting for the 1" pipe, but it was looking like small bends worked better than trying to get a big S-bend to go up from the "project bike" pipe to the Husqvarna Muffler. I quickly decided to just go all the way forward to the first U-bend as I had on the Lifan 125 Husqvarna.
The 1-1/8" steel tubing fit inside the 1-1/4" 0.065" wall mild steel tubing very nicely, with just a bit of wiggle to fine tune the angle of the fitting. I put two bends in a piece of the 1-1/4" tubing to get it to tuck in as well as possible and to angle down into the first U-bend of the 1-1/8" pipe. I also mounted the 1985 Husqvarna muffler lower on the Lifan 150 than my father had mounted the 1986 Husqvarna muffler on the Lifan 125. Instead of modifying and drilling the air box mount as he had done I just bolted the muffler to the existing bolt hole on the bottom of the air box mount. This seemed to work out very well, and I actually got the muffler to tuck in much better.
In just a few hours I had the 1-1/4" tubing bent, cut to length and welded to the U-bend. When I fired the bike up I was very impressed with how quite it was. The 1-1/4" tubing had gone into the Husqvarna muffler as intended, with a nice tight square fit. The 1" tubing on the Lifan 125 had been loose in the muffler fitting, so I extended it farther inside the muffler core. The smaller 1" tubing also ended up going into the core of the Husqvarna muffler a bit crooked so the exhaust blew unevenly on one side. I thought that this crooked exhaust entry was causing the Lifan 125 to be louder, so I cut the end of the 1" tubing off and welded a 4" long piece of the 1-1/4" tubing on to smooth the transition into the muffler. Interestingly this did not make the Lifan 125 Husqvarna any quieter, it is still a whole lot louder than the Lifan 150 Husqvarna at all engine speeds from 3,200 to 9,000RPM. The 1-1/4" transition piece did however seem to improve power and torque very slightly on the Lifan 125, so the crooked 1" tubing was causing some slight problems.
The Lifan 150 was dramatically quieter with a muffler installed, and amazingly it ran quite a lot better also on the same gasoline. I had been expecting that the 30" project bike pipe might have been too short, and that was a big part of why I wanted to run the new exhaust system on the same day on the same gasoline. Sure enough midrange torque did improve with the new quieter exhaust system, even onexactly the same gasoline. The Lifan 150 Husqvarna seemed to be running better at all engine speeds.
The next thing I did was to carefully compare the HD27B needle in the HongDa carburetor to the PZ27 needle in the HS Japan carburetor. They are very similar, but there is one signifcant difference. The taper starts farther down on the HD27B needle, and the HD27B needle is longer overall. The taper on teh HD27B needle starts about 0.06" farther from the lower needle clip groove than on the PZ27 needle. What this means is that the second needle clip position on the PZ27 needle is much closer to the third needle clip position on the HD27B needle. The needle clip possitions appear o be 1mm appart, so that 0.06" longer distance out to the start of the taper actually might be more like one and a half needle clip positions. i had been running the HD27B needle in the 24mm "27mm" HongDa PZ27 carburetor on the Lifan 150 in the second position, which might be even leaner than the first position on the PZ27 needle in the 24mm "27mm" HS Japan carbureor on the Lifan 125. I had run the Lifan 125 with the PZ27 needle in the first clip position quite a bit, and this had sometimes worked fairly well in warmer conditions on somewhat higher energy density gasoline. Lately though teh Lifan 125 has only been able to run with the needle clip in the second position, so I had the Lifan 150 set with a considerably leaner mixture at 1/5 to 1/2 throttle openings.
I moved the needle clip on the HD27B needel to the third position, which is fairly close to teh same as the second position on the PZ27 needle in the HS Japan carburetor. With the needle clip position richened up the Lifan 150 pulled even harder. For the first time it actually seemed to be working. Torque was more instant through the midrange, and stronger also. I was actually able to yank up some wheelies in second gear up a little hill. yes, much improved midrange torque. The engine actually seemed to be working, giving a bit of a bark and nice torque all the way down to 4,000 and even 3,500RPM.
The torque was more instant when riding, and the engine was able to make torque right away when fist fired up also. With the clip in the second position on the HD27B needle, even with the fresh gasoline and the uffler installed, there had been stumbling for 30 seconds or so after firing the engine up. Even when the engine had only been shut down for a few minutes and was stil warm to the touch there was still a substantial 15 second or so period of stumbling and lack of torque before it would run and pull from 3,500 to 5,000RPM. After moving the clip on teh HD27B needle to the third position the Lifan 150 was able to pull out and make torque right away at all engine speeds from 3,500 to 8,000RPM at an ambient temperatuer of about 47 degrees Fahrenheit.
Again I took the hand held chart plotter out to see just exactly what engine speeds the Lifan 150 was running at. What really amazed me was that torque was seeming good in third gear all the way down to 22mph and even 20mph. That's all the way down to 3,500RPM . Bellow 20mph in third gear torque fell off dramatically and the engine got very weak sounding with even some stumbling. At 20mph and above in third gear though it was smooth consistent torque that was seeming close to what a 150cc engine should be able to do. The power still took off quite a bit at around 38 or 39mph (6,600 or 6,800RPM), but it was not as much of an off-on hit as it had been earlier. There was a ctually good usable torque everywhere from 3,500 to 6,500RPM, and then the big power was still coming up at 7,000 to 8,900RPM. The power was also not seeming to drop off from 8,500 to 8,900RPM like it had been before. No, the power was continuing to build all the way up to 8,900RPM where it seemed to turn off all of a sudden. It seems like there is a rev limiter at about 8,900RPM the way the power just stops all of a sudden. if the 54mm stroke length Lifan 125 can make power to 10,000RPM then it would be expected that teh 59mm stroke length Lifan 150 would be able to make power to at least 9,200RPM and even slightly higher. Instead the Lifan 150 seems to be turning off all of a sudden at 8,900RPM with a rev limiter. It is true that the 27mm intake valve is far too small for the Lifan 150, the 27mm intake and 23mm exhaust vavles are the same as on the square 54mm bore by 54mm stroke Lifan 125. And worse the same cylinder head with the same 27mm/23mm valves actually very easily goes on teh smaller 52.5mm bore of the older 119cc Lifan 125 or the 107cc Honda 110. The 27mm intake valve is severely undersized for the Lifan 150, but the Lifan 150 does have that giant camshaft with about 40% more valve lift than the camshaft in the Lifan 125. It seems clear that the Lifan 150 should be able to make power somewhat beyond 9,200RPM if the Lifan 125 makes power to 10,000RPM and revs to 11,000RPM.
Anonoying rev limiters aside the Lifan 150 Husqvarna was actually sort of working. The jump from first up to second was still huge, but with good torque all the way down to 3,500RPM riding around on flat ground worked just fine. The huge jump from first to second is really a big problem, as it means that the correct gear for many steep hills is missing. it is like first gear works great, is plently low as it should be, but second gear is missing and instead all that is available is third gear which is too tall to get up steep hills. Just for casually cruising around on mostly flat ground though the huge jump is not all that annoying if the engine will pull second gear down to 4,000 and even 3,500RPM. What the huge jump does mean is that there is less shifting required to casually ride the bike, and under some circumstances that can be highly desirable.
Forth gear with the 17/50 gearing was also working great with teh engine torquing down to 3,500RPM. All the way down to 27mph in fourth gear (3,500RPM) the bike rode along nicely, with nice consistent torque to pull up to higher engine speeds effortlessly (although slowly) on flat ground. Down at 25mph fourth gear did not work, with chugging vibration and absolutely no torque.
In second gear the Lifan 150 Husqvarn will go down to 8mph with the 17/50 gearing, but lower it has a very hard time and sometimes loads up and stalls if speeds below 8mph are attempted for more than a few seconds. It seems that the all-at-once advance from 9 degrees BTDC to 14 degrees BTDC is at about 1800RPM. For some reason the engine is having a very hard time running down at this 9 degree BTDC spark timing value, and this may be related to teh occasional hard starting and stalling at low idle when cold. Perhaps the spark energy is also dropping off too much down at low idle. The engine always fires right up, but it stalls over and over again at low idle when cold. SOmetimes it has even been hard starting when warmed up, taking way too many big kicks to get it going.
WHen I had the timing light on the Lifan 150 I had noticed that the spark timing advanced rapidly up from 14 degrees BTDC to about 20 degrees BTDC, but then it was much more gradual up to 25 degrees BTDC at 6,000RPM. It is a two step advance curve, with a steep advance up to 3,500RPM and then only a small amount of additional advance out to 6,000RPM. The steep drop off in spark timing bellow 3,500RPM is so severe that it tends to cause some stumbling around 3,000RPM on weak gasoline. That steep drop off in spark timing bellow 3,500RPM is however not nearly as abrupt as the all-at-once advance at 3,200RPM on the Lifan 125. When that all-at-once advance drops down a huge 9 degrees of crankshaft rotation all-at-once large problems are almost certain. The smooth, although steep, advance curve up to 3,500RPM is much less likely to cause stumbling or other severe problems.
There are a lot of problems with the CDI control unit on the Lifan 150. Arguably the worst problem is that it seems to casue hard staring and stalling bellow 1800RPM. It always seems to be able to idle down very low if I turn the idle stop out, so it's not like it can't run at all down there. It has just had somewhat of a hard starting problem and seems much more prone to stalling in gear at very low engine speeds than the Lifan 125 Husqvarna. The little 150cc engine is easy to kick over, but when it takes dozens of kicks to get it to start that is a large problem. it always fires up very easily when rolled down a hill, and overall the bike is rather light and easy to push up a small hill. It can always be started, but hard starting requiring lots of kicks is extremely annoying. The Lifan 125 on the other hand just fires right up all the time, even with a substantially smaller kick. Sometimes with the throttle closed and no choke, sometimes with the throttle closed and the choke on, sometimes with the throttle cracked open and no choke and sometimes with the choke on and the throttle cracked depending on ambient temperatuer and what sort of partially flammable liquid happens to be in teh carburetor bowel, but it always fires right up on the first, second or sometimes the third kick.
Th other big problem with the Lifan 150 is the additional advance from 3,500 to 6,000RPM. That just can't work on such a small engine. An advance curve like that could be very useful on a giant four inch bore engine, but on a two inch bore engine it is totally inappropriate. i probably won't be using additional spark advance from 3,500 to 6,000RPM on the Lifan 150. By some miracle that can of slow flame front travel speed regular gasoline was able to sort of work on the Lifan 150, but the chances of additional advance from 3,500 to 6,000RPM reliably working on a two inch bore engine are extremely slim. I suppose I should keep an open mind and consider the possibility that normal regular gasoline really does have that slow of a flame front travel speed, but all evidence seems to be contrary to this idea. The slowest flame front travel speed gasoline I have ever seen will sort of work in the 98mm bore Husqvarna 610, although it is difficult to tune and prone to cutting out at 6,500RPM to 7,500RPM. On that gasoine four inch bore engines really need additional spark advance all the way up to maximum engine speed. Most normal gasoline has no difficulty revving out in the 98mm bore Husqvarna 610, but that does not mean it is spectacularly fast flame front travel speed gasoline or spectacularly powerful gasoline. It just isn't extremely unusually slow or weak.
Generally the gasoline has been very weak lately. I have hardly ever gotten any harshness out of the Lifan 125 at any engine speeds down to 3,200RPM, which seems totally wrong. On normal gasoline even the three inch stroke length Husqvarna 610 running 18 to 22 degree BTDC spark timing gets noticeably rather harsh as the engine speed is reduced bellow about 3,200 or 3,400RPM. The fresh 87 regular that ran in teh Lifan 150 without cutting out was a bit more normal. The Lifan 150 was giving a sizeable bark down at the bottom at 3,500 to 4,000RPM, but it was not excessively harsh and teh torqeu was good. The Lifan 150 is running hardly more than 20 degree BTDC spark timing from 3,500RPM to 4,000RPM, so that helps out considerably with strong and smoth torque down to those low engine speeds compared to the 25 degree BTDC spark timing on the Lifan 125. The longer 59mm stroke length of the Lifan 150 also would tend to mean smoother torque to slightly lower engine speeds, but the difference in stroke length from the Lifan 150 to the 54mm stroke length of the Lifan 125 is very small. The 76.5mm stroke length Husqvarna 610 as a dramatically longer stroke length than either the Lifan 125 or the Lfian 150.
Part of this is just that minimum engine speed does not tend to be amazingly similar for gasoline engines of any stroke length. The absolute bottom tends to be somewhere around 3,200 to 3,500RPM regardless of stroke length. The stroke length does however make some small difference. Longer stroke length engines do have to run down slightly lower, if for no other reason than they won't rev out as far on the other end. The Lifan 125 running without harshness at 3,200RPM with 25 degree BTDC spark timing seems irrational. A few degrees less spark advance would help a lot, but no matter how it is stacked making torque from 3,200 to 3,500RPM with a two inch stroke length is going to be somewhat harsh. With 20 or 22 degree BTDC spark timing it might just be extreme levels of barking gnarlyness and still fairly good torque down to 3,500RPM with the 54mm stroke length, with 25 degree BTDC spark timing though it would tend to be extreme harshness that actually dramatically reduces torque production. The barking gnarlyness is the result of a rather short stroke length and does not necessarily cause huge problems. The extreme harshness on the other hand is caused by earlier times of late compression ignition at low engine speeds due to excessive spark advance. It is the harshness from earlier times of late compression ignition that dramatically reduces torque down in the 3,000 to 5,000RPM range of engine speeds, and it is also this harshness that is so extremely hard on bearings and other internal engine components. The total lack of any harshness (or even any barking gnarlyness) way down low with the 25 degree BTDC spark timing on teh 54mm stroke length Lifan 125 clearly indicates a serious problem with the gasoline. On normal gasoline though there would be a serious problem with the spark timing. The 25 degree BTDC spark timing is too early for the little 125cc engine, and some sort of severe problem is practically garanteed. Still though 25 degree BTDC spark timing is clearly far superior to 27 degree spark timing, and the Lifan 125 has been running and making fairly good torque even when it has occasionally gotten rather harsh down low bellow 4,000RPM.
When that first company refused to supply the carburetor jets of the sizes they were advertising I ordered replacements from another company. These were even cheaper at $1.75 each, but the minimum shipping charge was $8 via USPS Priority Mail. That seemed fine at this point, as I was tired of waiting around forever for jets that showed up the wrong size. I ordered two each of the 93, 95, and 98 size of Keihin 99101-393 series jets. When they arrived they had different markings on them than the Keihin jets, but they were substantially the marked sizes. The Keihin jets have the Keihin symbol and the size stamped on the side, where these new replacement jets just have the size stamped in two places on teh large flat end.
The sizes differ from the stamped sizes by only a very small amount, but I could tell that there was some variation. The 0.0382" drill stock end of teh #61 drill went easily into both 98 jets, but the 0.0384" shank of the #61 drill fit tight and would not go all the way through. Both 98 jets seemed exactly the same, and I would say that the holes in them are very close to 0.975mm in diameter. The 0.0367" drill stock end of the #63 drill just starts into both of the 93 jets, but goes into one a bit farther than the other. The 0.0368" shank of the #63 drill won't go into either of the 93 jets. They are substantially 93 size jets, but they certainly are more like 0.932 to 0.934mm and not 0.930mm.
The 95 jets I couldn't easily get as acurate a measure on, as none of the standard size drill bits are exactly that size. The 0.0368" shank of the #63 drill drops right through both 95 size jets with a small bit of noticeable side to side wiggle. I could measure the angle of wiggle, but then I might only be measuring the variation in diameter instead of the actual diameter. The 0.0375" drill stock end of the #62 drill won't start in either of the 95 jets at all. Certainly the 95 jets are smaller than 0.953mm and larger than 0.940mm. Judging from the fact that there is some substantial wiggle of the 0.0368" drill stock in teh 95 jets I would say that they are closer to 95 than 94. They certainly are 95 size jets and not 93 size jets as both of the genuine Keihin 99101-393 series 95 labeled jets I was sent are.
Now I have the full spread of jet sizes for the 24mm "27mm" PZ27 carburetors. i suspect that the 95 size jet is the correct size for that carburetor, although on normal regular gasoline the 93 size jets may in fact work a bit better. What has to be kept in mind with these little engines is that what seems like a very rich mixture might in fact not be all that rich. With tons of spark advance on a small bore engien large amounts of the gasoline are being burned in flame front travel combustion before late compression ignition takes place, and this does strongly favor a mixture on the lean side for a variety of reasons. The big thing about running so much spark advance on a small bore engine is that it requires a substantially low compression ratio compared to the maximum compression ratio for the gasoline being used. This substantilly low compression ratio can then easily get into a situation where the gasoline won't pop off on late compression ignition at all. Too rich of a mixture displaces more intake air and lowers maximum attainable cylinder pressure even if gargantuane amounts of spark advance are used. Small bore engines with low compression ratios that won't rev up and make power even with huge amounts of spark advance sometimes benefit from a leaner air/fuel mixture, or at least an ideal air/fuel misture as opposed to an extremely overly rich air/fuel mixture that blackens the exhaust and might make a slight bit more peak power on a higher compression ratio engine.
The Lifan 125 is advertised as having a 9.47:1 compression ratio, and the Lifan 150 is advertised as having a 10.0:1 compression ratio. I doubt they are that high. I have swapped the same gasoline back and forth between the Lifan 125 and the 1991 Husqvarna WXE 350 with the 9.7:1 386 stroker motor, and both engines run fairly well on the same gasoline. The thing is that it was some extreemly low pressure gasoline that was running extremely crisply with instant torque at all engine speeds from 3,000 to 8,000RPM and even some light surging at 6,00RPM with the static timing setting at 21 degrees BTDC. That is very low pressure gasoline, no doubt about it. That same gasoline ran with no surging or whining what so ever, no excess harshness at any engine speed and absolutely no hint of needing a lower compression ratio in the Lifan 125. An 85mm bore engine running 21 egree BTDC spark timing certainly has a substantially higher compression ratio than a 54mm bore engine running 25 degree BTDC spark timing. There is no way around that. On top of that the 386 stroker motor has a much bigger 245 degree at 1mm valve lift camshaft installed advanced only about one degree of crankshaft rotation from straight up. The Lifan 125 has a much shorter duration camshaft with a considerably earlier intake valve closing time. Down at around 3,000 to 5,000RPM the approximately 8 degree earlier intake valve closing time of the Lifan 125 is absolutely going to yield slightly higher cylinder filling. it seems that the compression ratio of the Lifan 125 has to be a whole lot lower than the 9.7:1 of the 386 stroker motor. So add that to the list of transgressions on the Lifan 125 motor, they are lying about the compression ratio.
The Lifan 150 on the other hand does have a substantially higher compression ratio than the lifan 125. The intake valve closing time is nearly exactly the same, and teh 56.5mm bore is only very slightly larger, but the Lifan 150 does run considerably less spark advance at 3,500 to 4,500RPM.
With the Lifan 150 running at it's best with nice barking torque down low and fairly good power all the way out as high as it normally revs I swapped the gasoline into the Lifan 125 Husqvarna. I rode the Lifan 150 Husqvarna around to fully use up the gasoline in the carburetor bowel, and then at the end of the ride I drained a quart of gasoline out of the tank. I then drained allthe gasolien out of the Lifan 125, tippping the bike over to get the last pint out of the left hand side of the tank. I put the quart of gasolien out of the Lifan 150 Husqvarna in the Lifan 125 Husqvarna and took it for a ride. After riding around for several miles to use up the gasoline in the carburetor bowel the Lifan 125 Husqvarna was running great. About as well as I have ever seen it run. It was mostly just full flame front travl mode down low at 3,200 to 4,000RPM, but torque was seeming reasonably strong down there anyway. Then the Lifan 125 Husqvarna was giving a little bark and pulling darn well at around 4,000 to 5,000RPM. Torque did increase more up above 7,500RPM as usual, but it was not as dramatic of an increase in torque as I have often seen on teh LIfan 125 Husqvarn. Power was pretty good up on the top end, but most importantly torque war very good in the midrange. The Lifan 125 was also quieter than it had been most of the time. Espeially down bellow about 4,000RPM it was really very quite, no doubt because it was just running in full flame front mode much of the time at the lower engine speeds.
The most important thing here is that both of the Lifan motors do run at their best on the same gasoline. The other obvious conclusion is that the Lifan 125 has a much lower compression ratio than the Lifan 150. The Lifan 150 has a bigger bore diameter and runs less spark advance but still pops off more easily on late compresion ignitoin and barks big torque all the way down to 3,500RPM.
It is a lot less spark advance on the Lifan 150. Just 20 degrees BTDC at 3,500RPM on the Lifan 150 versus 25 degrees BTDC at 3,500RPM on the Lifan 125. Or something close to that, I found top dead center just by feel with a screw driver through the spark plug hole, so it could be off a degree or so in either direction. It is close to that though, I have lots of experience with marking small flywheels to find top dead center and the spark timing values. The Lifan 150 might have a very small 3" flywheel, but that ain't nothing compared to trying to time one of my points ignition Husqvarnas on the 0.9" diameter cranksahft. The Lifan 150 certainly does run substantially less spark advance than the Lifan 125 at 3,500RPM, there is no doubt about that. On such a small engine four or five degres less spark advance is a big deal. A very significantly larger amount of gasoline will burn in flame front travel combustion efore late compression ignition occurs with a spark timing value of 25 degrees BTDC in a 54mm bore engine than in a 56.5mm bore engine running 20 degree BTDC spark timing.
I can't stress enough what a huge difference that is in a two inch bore engine. Just how much of a compression ratio difference it would make depends on the type of gasoline being used. Slower flame front travel speed gasoline hides this spark timing difference because less of the gasoline burns in the short period of time between the fireing of teh spark plug and the time of late compression ignition. At least that is true on a four inch bore engine running 20 or 25 degree BTDC spark timing. A two inch bore engine running 20 or 25 degree BTDC spark timing burns a much larger portion of the gasoine in flame front travel combustion before late compression ignition takes place, even when the flame front travel speed of the gasolien is substantially low. i would say that even on the slow flame front travel speed version of the unusually weak speialty gasoline that the two inch bore engines buren a substantial amount of the gasoline in flame front travel combstion before late compression ignition takes place.
When the two inch bore engines stumble they just are not fireing at all, they are missing and they won't make any torque at all. When the two inch bore engines run in full flame front travel mode at around 2,500 to 5,000RPM they run fairly well, torque is weak and efficiency is low, but they still run well and move along. In these small engines late compression ignition only provides a certain modest increase in torque and efficiency at 3,500 to 5,000RPM, where in larger engines like the thre inch stroke length Husqvarna 610, full flame front travel mode is dramatically weak at all engine speeds above about 3,000RPM. The Husqvarna 610 motors don't normally stumble or stall when they hesitate, they just severely lack torque and efficiency. When the little Lifan 125 and Lifan 150 motors stumble they won't run at all and will load up and even stall if they don't get going within a few seconds. That is not to say that the Husqvarna 610 motors never stumble and stall on very weak gasoline, I have seen it happen a few times. That is not hesitating though, that is not running at all. I have ridden the Husqvarna 610 motors through the mountains many times for hours on end with horrible hesitation all over the place and never the slightest hint of stumbling or stalling. Hesitation in the Husvarna 610 motors causes a dramatic loss of performance, unbelievably high fuel consumption, darkens the lube oil, gunks up the exhaust valve seats and generally pisses me off to no end, but it has almost never caused even small amounts of stumbling or stlling.
With the 1-1/4" tubing "pipe" connected up to the Husqvarna muffler the Lifan 150 really was running a lot better. I rode it around several days in a row, and it continued to make torque without stumbling. Sometimes I noticed that after coasting or cruising casually the torque was not quite as immediate down at 3,500 t0 4,500RPM. It was still torquing down there without any stumbling, but there was no bark and not quite as much torque. Once fully warmed up after a few gib pulls though it was quite reliably torquing all the way down to 3,500RPM with a substantial little bark.
The Lifan 150 als continued to rev out fairly well, and when I really went after it with the muffler on it did pull to just over 40mph in seond gear. Wow, that's 9,600RPM, and there did not seem to be much of any drop off in power all the way up there either. The Lifan 150 CDI control box might actually back off on the spark timing a slight bit beyond 8,000RPM, but it is not a hard rev limiter. With the engine running strongly it certainly will pull out to nearly 10,000RPM.
Very small gasoline engines certainly could benefit from an advance curve that backs off slightly towards higher engine speeds. I would not expect the Lifan 150 to be quite small enough to benefit from this type of backwards advance curve, but when it is running reasonably strongly the Lifan 150 is able to rev all the way out fairly well despite and apparent slight backing off on the spark timing up at the top. In all reasonablness 9,600RPM is about as high of an engine speed as full power could be expected at for the undersized 27mm intake valve on the 56.5mm bore diameter and rather early intake valve closing time of the 250 degree at 1mm valve lift 100 degree lobe center camshaft installed five degrees advanced.
As far as the Lifan 150 CDI control box advancing from 20 degrees BTDC at 3,500RPM up to 25 degrees BTDC at about 6,000RPM; I still think that is a very bad idea on such a small engine. It is a rather gradual advance beyond 3,500RPM, but any amount of additional spark advance past about 3,500RPM or 3,800RPM in this size engine is something that would seem to cause large problems.
When I finally got around to swapping the gasoline out of the Lifan 150 Husqvarna into the 12.2:1 hot rod 610 Husqvarna motor I was somewhat surprised to find that they would both run fairly well on the same gasoline. I started out by ridding the 1991 Husqvarna WMX 610 with the 12.2:1 hot rod 610 motor around a bit on the old 91 (RON+MON)/2 octane rating premium gasoline that had been sitting in the tank for a few weeks. It ran pretty well, with strong instant torque down to 3,500 and 3,000RPM with only a small amount of harshness down there, and it also revved out to over 7,500RPM very easily with no cutting out of any sort. Torque wa smooth and powerful from 3,200 to 6,000RPM, and then it took off with authority above 6,000RPM. It was not the off-on sort of hit at 6,000RPM that I had been experiencing sometimes in past months on the 12.2:1 hot rod 601 motor, but just a substantial increase in power output above 6,000RPM. I didn't notice the cranksahft wiggle advance at 7,000RPM at all, although a lot of the time I found that I was revving only up to 7,000RPM before shifting. There was no surging or whining at any engine speed. The static timing setting was 18.5 degrees BTDC when I checked it after the short test ride.
I the fired the Lifan 150 Husqvarna up with the 87 (RON+MON)/2 octane rating regular gasoline in the tank. The Lifan 150 Husqvarna also ran pretty strong, with about as much power as I have ever seen it make. Once fully warmed up the little Lifan 150 was barking down to 4,000 and 3,500RPM nicely, but it was a bit reluctant to pop off at those low engine speeds. After coasting down a hill it was jsut full flame front travel mode at 3,500 to 4,500RPM. There was no stumbling of any sort, but the low end torque was a bit weaker and the bark was absent. Each time I went after it though I was able to get the extra barking torque down to 4,000 and 3,500RPM. The barking torque down to 4,000 and 3,500RPM was quite reliable, but not necessarily instant if the motor was cooled off a bit from cruising and coasting. The other thing that I noticed was that the Lifan 150 was seeming overly crisp at 6,500 to 7,500RPM. It ran and made power at all engine speeds from 3,500 up to over 9,000RPM, but I could really feel that incrorect advance curve delivering more spark advance at 6,000RPM than at 4,000RPM. The engine was somewhat reluctant to get going and make torque at 4,000 to 5,500RPM, but even at rather small throttle openings it took off screaming at around 6,500RPM.
After a sufficiently long test ride to fully use up the gasoline in the carburetor bowel I came back and drained a gallon of the 87 (RON+MON)/2 octane rating regular gasoline out of the Lifan 150 Husqvarna and put it in the empty tank on teh 1991 Husqvarna WMX 610 with the 12.2:1 hot rod 610 motor. The hot rod 12.2:1 motor ran extremely similarly on the regular out of the Lifan 150 to how it had been running an hour earlier on the old 91 premium. It felt like the regular actually had a slightly lower energy density, as I noticed more popping out the exhaust on deceleration and teh sound of the engine was a bit different. The torque also seemed a slight bit lower, although really it was running extremely similarly. I thought the gasoline out of the Lifan 150 Husqvarna seemed to actually have a slightly higher temperatuer of combustion potential, but a loer energy density. Torque was stil lfairly strong and smooth from 3,000 to 6,000RPM, and the power was still hitting right at 6,000RPM each time. The engine continued to make power to 7,900RPM with no cutting out. Power was not dropping off at 7,900RPM either, and it felt well able to rev farther. Again there was no surging or whinning of any sort. Just smooth and powerful torque right up to 6,000RPM where the engine took off and gave a substantial yank. Even the slight surging around 4,500 to 5,500RPM that I had experienced when I had swapped the gasoline out of the Lifan 125 into the 12.2:1 hot rod 610 motor in previous months was totally gone. On the Lifan 150 fuel there was no surging at all in teh 12.2:1 hot rod 610 motor, not the slightest bit. This gasoline certainly had a substantiallly lower energy density than normal gasolien from teh past three decades, but it wasn't as dramatically low energy density as the garbage I had often been getting from early winter 2015 to late fall 2016 either. No, this gasoline out of the Lifan 150 was actually working with the leanest needle clip position on the K32 needle in the 40mm DellOrto. Torque was fairly reasonable at 3,000 to 40,000RPM at small 1/4 to 1/3 throttle openings. Up at 4,000 to 5,000RPM a big twist up onto th richer 178 size main jet did yield increases in torque, but it was a modest increase. The engine actually was running and pulling across a wide range of engine speeds at 1/4 to 1/2 throttle openings. After a somewhat longer test ride I checked the static timing setting, and it was looking more like 19 degrees BTDC.
I found it really quite amazing that both the Lifan 150 Husqvarna and the 12.2:1 hot rod 610 motor were able to run well on teh same gasoline. It is not so much that I would not expect the 150cc engine and the 577cc engine to be able to run on the same gasoline, but considering the extra spark advance from 4,000 to 6,000RPM on that stupid Lifan 150 CDI control unit it was sort of amazing that both motors were able to run fairly well. The 610 had absolutely instant torque down to 3,000RPM and considerable harshness bellow 3,000RPM, where the Lifan 150 was rather reluctant to make full torque down at 3,500 to 5,500RPM. Obviously the Lifan 150 would do a whole lot better with just one fixed spark timing value from 4,000 to 8,000RPM. The 12.2:1 hot rod 610 motor was able to run along well at very small throttle openings everywhere from 2,300 to 4,00RPM with the 19 degree BTDC static timing setting, but opening the throttle bellow about 2,900RPM resulted only in clattering banging harshness without much in the way of additional torque. Obviously the big 610 motor would do better with the spark timing backing off a bit bellow about 2,500 or 2,800RPM.
Really just about any gasolien engine does better if the spark timing backs off bellow abut 2,500 or 3,500RPM. It would be 2,500RPM for giant four inch stroke length engines or thre inch stroke length engines running on extremely low temperatuer of cmbustion potential gasoline. Shorter stroke length engines can have the advance curve shoulder up somewhat higher around 3,000 to 3,500RPM, although all the way up to 3,700RPM might seem to work well for hot burning gasoline in a two inch stroke length engiene. The important thing is that the advance curve shoulder be at a slightly lower engine speed than works well for late compression igniton with that stroke length on the gasoine that is actually to be used. If the advance curve shoulder is too high it can cause surging and poor power delivery. If the advance curve shoulder is too low it causes unnecessary harshness at low engine speeds.
For most engines it is only a small amount that the spark timing should back off bellow 2,500 or 3,500RPM. Just backing off 5 degrees of crankshaft rotation from 3,000 down to 2,000RPM makes a really rather huge difference on just about any gasolien engine of any size. Just how low the spark advance should continue backing off depends on the stroke length of the engine. Giant four inch stroke length engines benefit from the spark timing backing off all the way down to 1,000RPM, where a two inch stroke length engine would normally not need the spark timing to back off farther bellow 2,000RPM. Even under very light loads in full flame front travel mode a two inch stroke length engine does not normally run bellow 2,000RPM, although it might low idle way down at 1,800 or even 1,500RPM.
The difference between absolute minimum engine speed and minimum engine speed for late compression ignition is smaller on a shorter stroke length engine. But that does not mean that a longer stroke length engine is able to run over a wider range of engine speeds, quite the contrary. Minimum practical engine speeds in flame front travel mode are roughly proportional to stroke length, and maximum practical engine speeds also tend to be proportional to stroke length. The minimum engine speed for late compression ignition is however always somewhere right around 3,000RPM regarldess of stroke length. It is a bit lower for long four inch stroke length engines and a bit higher for two inch stroke length engiens, but not by much. The four inch stroke length engien runs all teh way down to 1,000 or 1,200RPM in full flame front travel mode and the tow inch stroke engine runs down to around 2,00 or 2,400RPM in full flame front travel mode. In late compression ignition mode though it might be a 2,500RPM minimum for the four inch stroke length engine and a 3,200RPM minimum for the two inch stroke length engine on very weak low temperatuer of combustion potential gasoline, where on more normal hotter burning gasoline it might be a 2,800RPM minimum for the four inch stroke length engien and a 3,500RPM minimum for the two inch stroke length engine. In full flame front travel mode twice as much stroke length means half the engine speed, in late compression ignition mode twice the stroke length means maybee a 20% reduction in minimum engine speed. The other important point is that a two inch stroke length engine actually runs a lot better at 3,200RPM in late compression ignition mode than a four inch stroke length engine does at 2,500RPM. A giant four inch stroke length engien running weak low temperatuer of combustion potential gasoline might be able to run down to 2,500RPM in late compression ignition mode, but it still doesn't run very well down there.
Bore diameters are also very important for full flame front travel mode operation, but mostly up at the upper end. Obviously a larger bore engine is going to tend to have a harder time in full flame front travel mode up at higher engine speeds. For minimum engine speeds in full flame front travel mode teh bore diameter is also significant, but not in such a dramatic way. A smaller bore engine might just growel a bit more down at the lowest possible mean piston speeds for full flame front travel mode operation. Obviously getting the spark timing close to correct for the bore and stroke dimensions, operating conditions and teh gasoline that is actually being used is required to attain best possible efficiency under light loads in full flame front travel mode. For a giant four inch stroke length engine that can't run down to low mean piston speeds in late compression ignition mode; full flame front travel mode operation is going to be of much greater importance. For a small two inch stroke length engine that has a rather low mean piston sped at 3,500RPM; full flame front travel mode operation is of secondary importance. The two inch stroke length engine might still benefit from being able to run under light loads from 2,500 to 4,000RPM and higher in full flame front travel mode, but most of the tiem the engine speed is just going to stay up above 3,500RPM where late compression ignition works well for making power.
Pretty much right away I ordered a new 8-pin CDI control box listed as being for both the Zongshen 155 and the Lifan 150. I knew as soon as I put the timing light on the Lifan 150 that first day and saw the spark advance more and more up past 5,000 and 6,000RPM that a different CDI box was going to be required. First I contacted teh company I bought the Lifan 150 from, but when after several days they had nothing meaningfull to say, I ordered the 8-pin ZOngshen155/Lifan 150 CDI control box from another company. It will probably have the same incorrect advance curve as the one that came with the Lifan 150, but as a first step just buying a new CDI unit seemed like the way to go.
It has been almost two weeks now since I got the order confirmation saying the new 8-pin controller had been pulled, boxed up and was shipping out. That's a long time for a $13 shipping charge for a half pound 2 inch by 3 inch CDI box from Michigan to California, even if it is the Christmas crunch time of the year. No tracking number had been provided, and I didn't feel like calling to harass them about shipping delays on a CDI box that probably wasn't going to work anyway. Now might be a good time to mention the irrationality of the USPS tracking numbers in general. For over ten years I had this intuitive sense that the tracking numbers were far too long, but I didn't really think about it much. Then last year I decided to see just how excessively long the 22 digit USPS tracking numbers really are. It turns out that it is a trillion unique individual USPS tracking numbers for each man, woman and child on the face of the planet. yes, that is a lot.
When the replacement 8-pin CDI box didn't show up I skipped right to the next step, a whole new ignition system. For $120 delivered it is a new flywheel, new stator with power coils, new trigger coil, new ignition coil, wiring harness, 5-pin CDI control box and even a kill switch! Being advertised for Lifan and YX engines and as having "no rev limiter" and "powerful spark even to low engine speeds" it seemed like it would have a good chance of working. A flywheel puller was easy (and cheap at $10 delivered), as teh 27mm left hand thread is a very common size used on a wide variety of Japanese dirt bikes.
But first, Christmas. Stay tuned for the 2017 Lifan 150 Husqvarna!
Despite the Holiday traffic the new ignition system was delivered quickly. It was shipped USPS Priority Mail 3-day on December 21st and came all the way across the country from Pennsylvania to California in just three days, arriving on Christmas eve ahead of the scheduled delivery date. it just sat thre in the locked mailbox until I got back on December 27th, which was the scheduled delivery date. The puller had also been shipped on the 21st, but via USPS First Class Package from Texas, and it did arrive on December 27th.
The nut on the 10mm crankshaft thread was very tight. Using an electric impact wrench it came right off (yes a right hand thread for a flywheel nut on the left side of an engine), but I was amazed that it had been torqued on so tight. The left hand 27mm by 1.0 pitch puller threaded perfectly into the flywheel, and the flywheel popped off unexpectedly easily as soon as I turned the wrench. it is a rather steep taper, or at least much steeper than the 3.6 degree taper that the Husqvarna flywheels use.
Wow, that stator that came on the Lifan 150 is small! hardly two and a half inches across the coils.
The new "TRC Ultimate Full [ignition] System" uses a larger flywheel with a 3.5 inch outside diameter, and it is also thinner and consideraby lighter at just 509g. The smaller 3.05" outside diameter flywheel that came with the Lifan 150 is much heavier at 658g.
When I pulled the old stator off the new one did not at first seem to fit. It stuck out too far, and the flywheel did not come even close to going onto the taper before hitting the stator. I knew right away though that there was something strange going on. The new stator had a seal in the center that fit over the crankshaft end, and there was also a large O-ring on the outside diameter. When I looked closely at the Lifan 150 I saw that there was a seam of about the same diameter as the outside of the new stator. It looked like another plate on the side of the engine. Probably oil behind that!
Sure enough when I took the bolts out and eased the plate off oil leaked out. I pushed the plate back in, and then tipped the bike over on it's side. When I pulled the plate off there was the cam chain, crankshaft sprocket and cam chain tensioner. I had never had a Japanese four stroke dirt bike bottom end appart, so this was all somewhat new to me. I have long noticed that the Japanese dirt bike engines seem put together all wrong, with the cam chain, ignition and sprocket all on the same side. This seems to make the engines larger and heavier than necessary. As I found on the Lifan 150 this incorrect orientation of parts also results in an awkward ignition stator mounting system.
The new TRC stator did go right onto the Lifan 150 as advertised. I was a bit surprised to find that the mount is not easily adjustable though. The two mounting bolt holes on the TRC stator are cut for countersunk head bolts, so there really is zero adjustment in the stock configuration. This could probably be changed, but in stock configuration the stator mounts in only one orientation to the motor. That's the spark timing, and you better like it because there ain't any easy way to adjust it. With all of the harassment I have gone through with highly changeable gasoline supplies and having to dramatically change spark timing practically every time I went to the gas station in 2014, 2015 adn well into 2016 this actually was starting to seem appealing to just have fixed spark timing that would rarely, if ever, be changed.
It might be expected that the spark timing could be adjusted by moving just the signal coil, as it is separately mounted to the stator plate on these ignition systems. Tht is however probably no something to count on. yes, a small change in spark timing might be attainable by moving the pickup coil relative to the stator, but don't count on it. Normally the pickup coil stays in the same orientation relative to the power coils, and the entire stator is turned to adjust the spark timing. A small change in spark timing might in some cases be attainable by moving the pickup coil relative to the power coils, but moving the pickup coil relative to the power coils could also dramatically reduce the spark energy at cranking speeds.. just how this plays out depends on the overall design of the CDI ignition system. If the control unit is capable of storing energy from the power coils and then firing the ignittion coil on demand then the orientation of the pickup coil relative to the power coils might not matter at all. It just depends on how the circuitry is actually setup. I always buy complete ignition systems.
The new TRC "Full System" turned out to be somewhat less than complete, but it of course took me awhile to figure out jsut what was wrong with it. The rest of the installation went very easily, all the connectors matched up, the wire colors matched up, and in just a few minutes I had the new ignition coil and "Racing" TRC red 5469 CDI control unit mounted on the Lifan 150 Husqvarna.
As soon as I kicked the Lifan 150 I could tell that the new ignition system was dramatically different. It kicked back, popped out the intake a few times and then after a few more kicks it fired up and ran. It was able to idle right away without stalling, but there ws stumbling at the first crack of the throttle. It felt extremely lean, but did not die. It kept running, and in about two seconds the stumbling was gone. The idle speed was noticeably much hgiher than it had been with the old system, and it sounded very weak and unstable. Thgat was actually easier starting than what I had ofen been experiencing with the ignition system that came on the Lifan 150.
The idle was very unstalbe and weak, but it never stalled in neutral. When letting the clutch out though it stalled very easily. It was starting more easily much of the time when warm, but sometimes it was just hell to start with lots of kicking back, poping out the intake and even flooding. A few times I had to give up on the kick starter after it flooded and just roll it down a hill. The idle speed was also up much higher, about 2,400RPM, as opposed to the stable 1800RPM low idle of weeks past. When I tried to turn the idle speed down it just got weaker and more unstable. It had to idle up at 2,400RPM to work at all.
When I rode the bike I was pleased to find no stumbling, but the torque was extremely weak at the lowest engine speeds. It wouldn't run at all bellow about 2,500RPM, adn the torque from 2,500 to 3,500RPM was very weak. Even from 3,500 to 4,000RPM the torque was seeming rather weak, but then it ran much better over a seemingly wide range of higher engine speeds. At 4,500 to 6,000RPM the torque sounded better, felt better and was also stronger than with the ignition system that came with the Lifan 150. It also revved out farther and made more power. Full power seemed to be reliably available all the way up to 10,100RPM. Certainly a vast improvement in terms of moving the bike along. I could actually shift between the gears while staing in the power. Most importantly though the strange feeling of hesitation at 4,000 t 5,000RPM followed by excessive crispness at 6,000 and 7,000RPM was mostly gone. Yes, that additional spark advance from 4,000 to 6,000RPM just really didn't work on the little Lifan 150.
When I put a timing light on the new TRC ignition system I found the starting and idling problem. At first I didn't know exactly what I was seeing, but the old Actron L100 timing light certainly was indicating poor ignition system performance. The timing appeared to be jumping back and forth a huge amount, especially at the lower engine speeds. As near as I could tell the spark timing was constant at all engine speeds, but the strobe was jumping around like crazy from 3,000 to 4,000RPM. Actually it was jumping around at all engine speeds, but when I revved it out it was much more stable and appeared to be reading the same spark timing value across a wide range of engine speeds. It looked like about 23 degrees BTDC or so, but all the jumping around was distracting and made it hard to pick a number.
I began to get the impression that the TRC ignition system was actually backing off on the spark energy from 1,500 to 4,000RPM. It fired fairly reliably at cranking speed, but then it would often stall once it started to rev up towards low idle speed. The torque at 2,000 to 2,500RPM was just so extremely weak that letting the clutch out anything less than very slowly caused the engine to stall. Much less torqeu at 2,000 to 2,500RPM than with the ignition system that came with the Lifan 150. it seemed like this TRC 5469 CDI control unit was using a reduction in spark energy in place of an advance curve. It was seeming like just one fixed spark timing value at all engine speeds, but backing off on the spark energy dramatically at 1,500 to 4,000RPM reduced harshness at those excessively low engine speeds for late compression ignition. It didn't work worth a darn. Yes, the harshness from 2,000 to 4,000RPm was absent, but so was the torque and the stability.
To test out the idea that the problem was weak spark energy at 1,500 t0 4,000RPm I closed up the spark plug gap a bit. The stock gap was 0.026", adn I closed it down to 0.020". This actually did make a noticeable difference. The engine became easier to start, at least when warmed up, and torque improved slightly across all lower engine speeds. The engine also sounded and felt a bit better around 4,000 to 5,000RPM. It was however a very slight difference. The biggest difference was really just somewhat easier starting when warm. That was good, but not good enough. The TRC ignition still did not work. It could be called a vast improvement over the 8-pin CDI ignition system that came with the Lifan 150, but that is not saying much. Neither of them worked.
Right away I had ordered some more 5-pin CDI control units. Once I got the TRC system I saw that it used the same 5-pin CDI connector as the Lifan 125, so there seemed to be some possibilities. I ordered a "blue" TRC "Racing" 5-pin CDI unit, and I also ordered another "Performance 5-pin" CDi unit that looked the same as the one on the Lifan 125. These were all very cheap. The prices had actually come down in recent months. The "Performance 5-Pin CDI" was $4.50 delivered, very cheap. It arrived in just two days, and it did indeed look exactly like the 5-pin CDI unit on the Lifan 125. It turned out to be very different though. It actually has an advance curve, or at least a three step advance that sufficiently approximates a smooth curve from 1,500 to 3,500RPM.
Wow, what a difference. Finally an ignition system. boy, that was difficult.
First I put the new CDI unit on the Lifan 150. Wow, torque at 2,300 to 3,500RPM, and smooth and quiet also. When I put a timing light on the Lifan 150 I found that the low idle spark timing was about 15 degrees BTDC, adn then it was advancing rather quickly up to 20 degrees BTDC as the engine speed increased. Maximum advance topped out at about 25 degrees BTDC, and this seemed to be comming around 3,500RPM. Then from 3,500RPM all the way up it was just one fixed spark timing value. No advancing, no rev limiter, and no jumping around. Even down at low idle speed and 2,500 t0 3,500RPM the strobe was reading steady.
Torque was dramatically better at 2,300 to 3,500RPM, much stronger than with either of the other ignition control modules, and also very smooth and quiet. I was amazed to be able to cruise along in fourth gear very nicely all the way down to 20mph. Then at around 3,500RPM the Lifan 15 took off with a bark and the torque increased quite a bit. Torque continued to increased up to 5,000 and 6,000RPM, but it felt much better and sounded much better. The increased in torque from 4,000 to 6,000RPM was smooth, and the feel was good. Extremely dramatically better than with the 8-pin CDI, and also much better than with the TRC 5469 CDI unit. Power up top was also good, and it pulled hard all the way up to 10,300RPM. Finally an ignition system that actually works. Wow, what a difference!
I switched back and forth between the new "Performance 5-Pin CDI" and the TRC 5469 CDI while I was out riding around. Big difference each time, not only in torque, but also in starting performance. The Lifan 150 was starting up with the TRC 5469 CDI unit, but it was taking a few kicks and sometimes it was very hard to start. IT was often popping out the intake and sometimes even kicking back. With the new "Performance 5-Pin CDI" unit the Lifan 150 was starting up on the very fist kick over and over again. A few times it took two or three kicks, but mostly it just fired right up on the very first kick each time. I switched back and forth many times to be sure. One time the Lifan 150 kicked back, then started and stalled, then kicked back again and finally flooded and would not start. I kicked and kicked many times, but I couldn't get even a pop out of it. I then switched to the new "Performance 5-Pin CDI" unit and kicked the bike. It fired right up on the third kick without even taking the spark plug out. Yes, a vast improvement.
I then took a quart of the gasoline out of the Lifan 150 Husqvarna and put it in the Lifan 125 Husqvarna and I also put the new "Performance 5-Pin CDI" on the Lifan 125. I left the old 5-pin CDI unit mounted to the Husqvarna frame, and just stuck the new unit on temporarily.
The low end torque was vastly improved on the Lifan 125 Husqvarna also. From 2,500 to 3,200RPM the torqeu was stronger than I had ever seen from the Lifan 125 on teh old CDI unit. Stronger and also smoother. Again I switched back and forth many times to make sure I knew what was going on with the Lifan 125. On this gasoline the old all-at-once advancing CDI unit was actually working fairly well. There was no stumbling, and just a bit of chugging around 2,500 to 3,000RPM. The dramatic difference was the torque. With the new unit the torque at 2,400 and 2,800RPm was much stronger, and also smoother. The chugging was gone, just smooth reliable torqeu in full flame front travel mode.
From 3,500 to 10,000RPM both black plastic 5-pin CDI units seemed exactly the same on the Lifan 125. With the 95 size main jet (actually 95 size) and the PZ27 needle in the leanest clip position the Lifan 125 was reluctant to get going on the top end on this 50 degree December evening. Once fully warmed up on some big pulls though top end power was available all the way out to 10,000RPM. Torque down at 4,000 t0 7,000RPM was absolutely reliable, and feeling rather strong. It was actually higher pressure gasoline causing the low compressino ratio Lifan 125 to be reluctant to make top end power. Down at 5,000 and 7,000RPM the Lifan 125 was able to take wide open throttle very reliably even when cooled off from cruising and coasting. And even down at those midrange engine speeds the torque did increase noticeably as I opened the throttle from 3/4 to wide open. This was 87 (RON+MON)/2 octane rating regular gasoline straight from the gas station that I ran in both Lifan Husqvarnas. In the higher comprssion ratio Lifan 150 with the same 95 size main jet (actually 95 size) there was no reluctance to rev up and make power on the top end on this regular straight from the gas station. It seemes somewhat weak and low energy density as has often been the case in recent months, but this batch is also higher pressure gasoline that is not as well able to work in the low compression ratio Lifan 125.
That's the good news. The bad news is that the new "Performance 5-pin CDI" unit with teh smooth advance curve appears to cause slightly harder starting when cold in the Lifan 125 Husqvarna. once warmed up the Lifan 125 was starting very easily on the very first kick on both CDI units. When cold though there was a noticeable reluctance to start and idle on the new "Performance 5-Pin CDI" unit. This is probably just due to unusually weak gasoline. As the Lifan 125 was warming up on the new "Performance 5-Pin CDI" unit it would take the first very small crack of the throtle and slowly rev up, but if I twisted the throttle a bit more it would stumble and die. Above about 2,500RPM it was able to take any larger throttle opening and rev up crisply, it was just down at low idle and slightly above that more than a miniscule crack of the throttle caused the engine to stumble. Putting the choke on removed this stumbling while cold, adn the off idle stumbling also totally went away once the engien was fully warmed up. In itself this little bit of stumbling off idle when cold on a cool December evening does not seem like any kind of a problem. It was absent with the choke on, and totally went away once the engien was fully warmed up. What was alarming was just that it was a bit worse with the new "Performance 5-Pin CDI" unit than with the old CDI unit. Is it weak spark at 2,000RPM? Or is it just that the new CDI unit backs off slightly more than 9 degrees of crankshaft rotation? I am guessing that it is actually just that the advance curve backs off fartehr, and this unusually weak gasoline is noticeably more reluctant to run lean with those two degrees less spark avance. A two inch bore engine really should have no difficulty running at 2,000RPM with 15 degree BTDC spark timing. That is actually a lot of advance for a two inch bore!
The next morning when I fired the Lifan 125 up again at about the same 47 degree ambient temperatuer it was unusually hard to start, taking more kicks than it has probably ever taken before. I switched back and forth between the two CDI units without letting the engine warm up much, and they were rather similar. The Lifan 125 wouldn't run on either one. Turning the choke on certainly got it going, but then it would begin to flood and die after just a few seconds with the choke on. With the new advance curve CDI it only took a second of the choke to get past that first little stumble just off idle, where with teh old all-at-once advancing CDI unit it just wouldn't run at all anywhere below 3,200RPM without the choke on. And then it would only run for two seconds with the choke on before starting to load up and die. There certainly was more of a reluctance to take a crack of the throttle just off idle with the new advance curve CDI. It backs off on the spark timing just that little bit more, and the spark energy might be weaker down there also. Overall it is a very slight difference, but it is noticeable on a cool morning with unusually weak gasoline. It seemed to take a very long time for the Lifan to warm up and run without stumbling. It was able to run and make power right away with the advance curve CDI, but each time I let the engien speed drop bellow about 2,300RP it would very annoyingly stumble. With the all-at-once advancing CDI unit it was perhaps slightly easier to pull out very slowly at low idle speed, but then it was extremely reluctant to accelerate past the 2,500 to 3,20RPM stumbling. Once warmed up the stumbling was fully gone with both CDI units, although the chugging weakness at 2,500 to 3,200RPM on the all-at-once advancing CDI unit never fully went away. Nine degrees of all-at-once advance i sjust far too mcuh, the engien won't take it.
The advance curve CDI also seems to be advancing too far. The eleven degrees of additional advance from 2,000 to 3,500RPM is way more than a 125cc or 150cc or even a 400cc engine should use. The little 125cc engine has a very hard time with that much advance, it just can't take it. On weak gasoline it won't run when cold at the lower spark timing value, and on normal gasoline it gets harsh at 3,500 to 5,000RPM with so much spark advance. The lower end around 15 degrees BTDC should work fine, in fact it probably doesn't need even that early of spark timing. Up at 3,500 to 6,000RPM though 25 degree BTDC spark timing is simply too early for a small engine. It just can't work.
In the end all that can be said about the CDI control units themselves is that they are advancing too far, there is too much difference between the low idle spark timing and the running spark timing. On certain types of gasoline that much spark advance can be made to seem to sort of work, but it is just extremely likely that either extreme harshness at 3,500 to 5,000RPM or stumbling and weakness at 2,000RPM will be aproblem with that much additional spark advance.
So I now have a 9 degree of crankshaft rotation at 3,200RPM all-at-once advancing CDI unit, an 11 degree of crankshaft rotation 2,000 to 3,500RPM advance curve CDI unit and the TRC "red" 5469 CDI unit that doesn't advance at all. None of them really work, although the advance curve CDI unit certainly does allow the engine to run and make torque well once it is warmed up a bit.
The stumbling down low at 2,000RPM when cold on weak gasoline can be cured by richening the jetting. jut then the engine is overly rich at the first twist of the throttle on normal gasoline. This is a common problem. Jetting changes can do a lot to mask ignition system problems, but hiding problems by creating new problems just results in lots of problems. At best very careful jetting can hide a certain amount of advance curve non-functionality without reducing peak torque production or peak power output. High fuel consumption and high emission are however practically garanteed when creative jetting is used to hide dramatic advance curve problems. And on top of that; overly rich jetting reduces an engines's ability to run over a range of altitudes. Fairly rich jetting at wide open throttle is good for making peak power output up to high mean piston speeds, but rich jetting at small throttle openings just causes problems. Lots of problems. High fuel consumption, high emissions, deposits in the combustion chamber, poor throttle response when hot and an inability to run well over a range of altitudes. If an engine has the ideal rich mixture to run at it's absolute strongest when cold in cool conditions with no choke then it is going to be drowning in gasooine once fully warmed up.
To further compound the problems there is no easy way to adjust the mixture at about 1/8 to 1/5 throttle openings on the slide type carburetors I have. The idle mixture screw adjusts the mixture at low idle, the pilot jet adjusts the mixture from just off idle up to about 1/8 throttle opening adn the main jet adjusts the mixture from 3/4 to wide open throttle. Everything in between is on the needle. The needle clip position adjusts the mixture at 1/5 throttle up to 3/4 throttle, and different needle tapers can do slightly different things within this 1/5 to 3/4 throttle range. A typical straight taper normally just richens up very slightly as the throttle is opened from 1/3 to 3/4, but changing the needle clip position sometimes changes this also. Generally moving the needle clip is a good way to richen or lean a carburetor in the 1/4 to 3/4 range of throttl openings, and with main jet changes it is usually failry easy to tune in this 1/4 to wide open range. That still leaves 1/8 to 1/5 throttle openigns though.
The 1991 Husqvarna Owner's Service and Tuning Manual says that a differnt slide shape is required to tune the 1/8 to 1/5 throttle openings on the DellOrto carburetors. This might sort of be true, but there is also something else that changes the mixture at 1/8 to 1/5 throttle, adn that is the fit of the shank of the needle in the needle jet. The problem is that needle jets are much more work to change than any other jet in a carburetor. At best it is sometimes possible to get a needle jet and needle as a matched set for a certain caburetor. That is great if it is the correct needle jet and needle for the gasoline tht is curretnly available. If the advance curve is wrong, or the gasoline is wrong then you are just shit out of luck. As far as standard carburetor tuning goes anyway.
Needle jets can be bored out larer, but you can't go back without a new one. Main and pilot jets can be soldered up if replacements aren't available, although even that can be difficult if the size you need happens to come out between standard drill sizes. Soldering up a needle jet though is not really an option. The needle rides on teh jet, a grass on brass (or aluminum on brass) bearing lubricated by gasoline. That works fine, adn they last a really long time. Solder is however mcuh softer and wears much more quickly. Add to that the fact that small changes in needle jet diameter make large differences in the mixture at 1/8 to 1/5 throttle and it is easy to see that needle jets are not so easy to modify. I havent ever drilled out or soldered up a nedle jet, and I don't have any desire to either. I check the needle jets to make sure they stay the same size, but that is as far as I have ever gone.
The 24mm "27mm" HS Japan and 24mm "27mm" HongDa PZ27 carburetors both appear to be on teh lean side at 1/8 to 1/5 throttl openings. they work perfectly on normal gasoline, adn even on weaker gasolien once the engine is warmed up. Most people would consider them too lean at 1/8 to 1/5 throttle openings. The PZ27 carburetors might be considered too lean, but that's just because they aren't dramatically too rich like most other carburetors.
The DellOrto carburetors on the 1991 through 2003 Husqvarnas are too rich at 1/8 to 1/5 throttle openings. Quite a bit too rich, like most carbureotrs. So rich that they will sort of work on extremely dramatically low energy density gasolien, even gasoline with 30% ethanol added in. That is way too rich. The DellOrto carburetors won't work on E85 or 100% ethanol though, they aren't that much too rich. I can run 100% ethanol in the 40mm DellOrto carburetors by leaving the choke on, but that dumps tons more fuel in all teh way up to 1/5 throttle where the needle clip position takes over. The coke on the DellOrto carburetors is like another little carburetor, with a jet and an air passage. Open the throttle farther and it sucks more air and more fuel through the choke bypass. This means a richened mixture all the way up past the pilot jet. Even up at 1/5 throttle the choke is dumping a bunch more fuel in, enough to get the engien to run on 100% ethanol with the K32 needle in the richest clip position.
The "24mm" Mikuni that came with the Lifan 150 has a bypass choke and a choke jet like that. It looks like a really nie little carburetor. The problem is that it doesn't come with jets. I just took one look at the extreme concave shaped needle and threw the thing in the parts bin. For one thing it isn't a 24mm carburetor. The slide measures 20.4mm in diameter, and the tall opening has the same cross sectional area as a 22mm carburetor. It is a nice carburetor, perhaps the perfect size for the Lifan 125. It just doesn't come with jets. That concave needle is a huge problem, they don't work. I have taken a few of those concave needles out, they just always cause a horrible rich spot around 1/2 throttle. The other problem with the 22mm "24mm" Mikuni is that it takes aMikuni jets, those annoying jets with markingst that don't seem to mean anything. I have never messed around with jetting Mikuni carburetors more than trying to find the correct needle clip positon to work with the stock main jet. On the 1980's Husqvarnas the 38mm Mikunis are too rich, but they work. The mikuni 400 main jet is a bit fat for the 38mm carburetor, but tey do work. They certainly dump plenty of gasoline in. That's good engough for a two stroke. The carbureted two strokes run so poorly that it is hard to tell what is going on with the jetting anyway. As long as they will start, idle and make power on the stock jetting then that is about as much as can be hoped for. The Mikuni 400 main jet in the 38mm Mikuni carburetors seems like about the same wide open mixture ratio as the stock 180 main jet in the 1991 Husqvarna WMX 610 40mm DellOrto. About as rich as has any chance of working. Any richer and every real measure of performance gets worse on normal gasoline. Extremely low energy density gasoline, like gasoline with 30 or 40% ethanol mixed in certainly can use fatter jetting. But that should be irrelevant. Fatter jetting than this never really yields significant power gains, it just allows 40% ethanol to be mixed in with less loss of peak power output.
The little 22mm "24mm" Mikuni is just like the 24mm "27mm" PZ27 carburetors in that they all have an idle mixture screw and a pilot jet. The bigger Mikuni carburetors on the 1980's Husqvarnas just have an idle jet, no pilot jet. That is a big difference if the setup is changed back and forth. For a stock carburetor that is just fun with the factory settings this difference doesn't necessarily mean much. Basically what it comes down to is that the big Mikunis on the 1980's Husqvarnas just have less adjustability than most slide type carburetors. That's fine if they work in stock form, but disaster if they need to be changed.
When I tried to top end the Lifan 150 Husqvarna it didn't seem to be making much power. At first it was pulling nicely in fourth gear at small throttle openings around 20 to 40mph, and it was very quiet. When I twisted the throttle more it gave a bark and seemed to accelerate effortlessly (if slowly) up to 50mph. I cruised along for a while at 35mph, and the engine seemed to get very hot. Even though it was a cool late December afternoon there was a lot of heat coming off of the exhaust. As the motor got hot the torque dropped off. It was taking a bigger twist of the throttle to cruise at 30 and 35mph, adn there was not as mcuh power available when I opened the throttle.
I thought something serious might be wrong, so I just cruised around for a while. When I went after it in third gear the power seeemed fairly good, and I was able to hit 52mph (9,000RPM). When I shifted to fourth th eLifan 150 Husqvarna slowly accelerated to 55mph (7,100RPM), and then I ran out of straight away. After riding fast for a while the engine again got hot and power dropped off. It would then only go 50mph in fourth gear and felt much more sluggish. When I rode on a smaller trail using full power in first, second adn third the power seemed better and the engine stayed much cooler.
When the engine got hot the torque had dropped off dramatically at very small cracks of the throttle downat 2,500 to 3,500RPM in full flame front travel mode. That means too much spark advance, no doubt about it. Power also dropped off up at higher engine speeds at wide open throttle when the engine got hot, which indicates that it was also running excessively crisply. The solution to both of these problems is less spark advance. Too bad the ignition system is not adjustable.
Since I have plenty of open class Husqvarna race bikes to ride I might not mind so much if the Lifan 150 Husqvarna is sometimes too crisp once fully warmed up at low elevation, but this is a tricky issue. An air cooled engine running excessively crisply is in grave danger of overheating when pushed hard, and that has historically been a large problem. Some form of adjustment on the spark timing would seem to be necessary. For a sophisticated electronically controlled CDI ignition system a map switch would seem appropriate. A stator that is easy to turn without pulling the flywheel off seens pretty good also, especially if the intention is to mostly leave it just at one setting.
On a points ignition bike I would have backed off on the spark timing today as soon as I felt the torque drop at 2,500 to 3,500RPM in full flame front travel mode. That was an obvious sign of excess spark advance. Of course I probably wouldn't have been running 25 degree BTDC spark timing on a 150cc engine either. I would probably draw the line at about 22 degrees BTDC on such a small engine. If it wasn't crisp enough once fully warmed up at 22 degrees BTDC it woudl get a higher compression ratio. The giant 577cc Husqvarna 610 motors seem just fine up to 24 degrees BTDC on normal gasolien, and can well handle 25 or even 26 degerees BTDC on weaker gasoline. Very small 125, 150 adn 200cc per cylinder engines though can't handle getting quite that close to the 25 or 27 degree BTDC earliest possible spark timing for the latest possible time of late compression ignition at 3,500 to 6,000RPM. And on top of that the 22 degree BTDC is really very early even for full flame front travel mode at 3,500 and 4,000RPM in a two inch bore engine on any sort of normal gasoline. A two inch bore is half as far across as a four inch bore, that is significant.