When I bought my first dirt bike at age 13 I already knew about Huqvarnas and desperately wanted one. The main problem was that I was a skinny 120 pound early teen and the Husqvarnas had never been available in kid's bike sizes. Eventually I did get the Husqvarna that I wanted, but not until many years later.
The Honda Substitute
Husqvarna at Long Last
The Kawasaki Substitute
Pointing to a Running Husky
Crankshaft Wiggle Advance
1991 WP Suspension Vs. 1992 Showa Suspension
What I really wanted was a four stroke dirt bike, but very few were available in the early 1990's and essentially none were available on the used bike market at the time. What I had to choose from instead were a 1979 or so Yamaha 175 dual sport two stroke, a water cooled Husqvarna 400 two stroke and the 1987 Honda CR 125 that I eventually purchased for $1000. The 175 Yamaha was a really nice easy to ride bike, but it made hardly any power for such a large two stroke. Even with nearly zero dirt bike experience I noticed the weak power delivery as soon as I took off on the test ride. As a beginner I could have been happy with the weak power, but all of the street legal accoutrements seemed really in the way on what was otherwise a rather compact dirt bike. I knew there was no way I was going to ride a two stroke on the highway. The Husqvarna 400 was a really nice looking race bike, and was the best deal around for only $800. The main problem was that the Husqvarna was too big, particularly in the engine department the race tuned 400cc two stroke was way more than I was going to be able to handle for some time to come. I was able to ride the big Husky though, and I very well might have bought it anyway if it were not for the hard starting problem that this particular example was said to have.
The Honda CR was much more appealing because it was very small and light feeling after ridding the big Husky, and it also started up easily on the first kick. The '87 CR 125 I bought was a retired race bike that had been ridden hard but was still in mostly decent condition. The main modification was a Pro Circuit pipe, which as it turned out did change the power character of the bike considerably. I knew it made some power up at high engine speed because the seller had ridden it around to warm it up before I took the test ride, and I could certainly recognize the sound and acceleration of a race engine. When I first rode the Honda two smoker I just idled around to get used to the suspension and the feel of the bike. I revved the engine up occasionally for the thrill of acceleration, but for the most part the CR was faster than I expected or really wanted at that time. Pretty quickly I began to have spark plug fouling problems, and it was taking a new spark plug to get the thing started each time I rode it. What I discovered after going through a dozen or so spark plugs was that the high performance two stroke did not want to be idled excessively. Keeping the spark plug from fouling required that higher power output be used a large portion of the time. As I got used to laying down a substantial portion of the power output from the little race engine much of the time I had no further trouble with spark plug fouling or starting difficulties. I did lean the needle clip position out one notch from stock as I normally rode up at 3,000 to 5,000 feet of elevation, and although this did not seem to make a dramatic difference the bike did work fairly well compared to other two stroke dirt bikes.
With the leaner needle clip position and all stock ignition timing settings the CR 125 was however very sensitive to changes in the fuel, and it would really only run on premium 91 (RON+MON)/2 gasoline. The real problem of course was the low 8.7:1 compression ratio, but back in the 1990's this was considered a reasonable compression ratio to run. The Pro Circuit pipe did allow quite a bit of power output up at the top of the engine speed range, and I was able to lay down enough power to ride with the 250 two strokes at least on the tougher technical trails. It did however take me several years to get to the point where I could ride the little 125 close to it's potential.
What I did not like about the little two stroke was that it used a whole lot of fuel. I got about 25mpg either on tight trails or on larger dirt roads, and this seemed pretty poor. The 250 two strokes could go just as far on a trail ride with only just a slightly oversize fuel tank. I wanted a four stroke dirt bike in the worst way, but availability was still spotty at best.
I was able to pick up a heavily worn 1985 Honda XR250 for just $750, but this only wet my appetite for four stroke dirt bikes. The '85 XR had the linkage rear suspension and did work quite well for some types of trail ridding. The biggest problem with the XR250 of course was it's extremely high weight. Coming from the CR125 the XR250 just seemed to weigh a ton. The suspension on the XR was also far too weak, and I tended to bottom it harshly even on the tightest first and second gear single track through the woods. The XR250 motor ran well, but was far from perfect. Power delivery was good, with excellent torque all the way down to amazingly low engine speeds around 3,000RPM and it would also rev up quite high. What the XR250 engine did not do though was make big power. Even up at the top of the engine speed range it was quite weak compared to the CR125. The suspension on the XR250 could have been beefed up with stiffer springs and a revalve, and the motor could have been augmented with a bigger camshaft and a slight bump in the compression ratio but there was nothing that was ever going to be done about the extremely excessive weight of the XR.
Eventually the CR125 began to seem too small for me also, and the suspension just was not up to the task of keeping up with the faster 250 riders. By the time I was of legal age my weight had climbed to 200 pounds, mostly in the thigh muscles, and I was able to make use of some of the extra power of 250 two strokes I rode. Despite my rapidly increasing size and strength I still wanted a light dirt bike, and I seriously considered just moving up to the 250 two stroke class. I even once looked at an old air cooled CR480 advertised for sale, but I just could not bring myself to buy such a fuel hog.
It was when I was working at my first real full time job that I finally had more substantial financial resources to pursue my dream bike. I had decided that it had to be a Husqvarna because they were the only lightweight high performance four strokes in existence. It was really a matter of choosing between a new Husaberg or a used Husqvarna. The slightly older early to mid 1990's Husabergs were rare as hens teeth, and the new late 1990's Husqvarnas were also hard to come by at dealerships. The new Husabergs were available, but little was known about them and there was a general feeling that they were way over priced at twice what a new Suzuki or Kawasaki cost. Certain older Husqvarnas from the early 1990's were also available, and this is the route I chose. My 1991 Husqvarna WMX 610 was advertised for $2500 and the seller had a small dirt lot across the street from his house for a test ride. The big Husky was a bit hard starting, and I was very disappointed that it seemed to run very poorly as well. It was not that it did not make power, because that it certainly did. It was just that the engine sounded like a poorly tuned lawn mower and heated up a lot. The WMX 610 was however just the bike that I wanted and I felt confident that I could sort out the simple and familiar single overhead cam four stroke engine. In light of the poorly running engine and overall rather rough condition of the heavily used bike I offered $1700, which the second owner happily took. He had not had the bike for long, and apparently the first owner had sold it because an engine rebuild at the dealership had turned out poorly. When I purchased the bike I did not even know that the Motorcycle Division of Husqvarna had been sold in 1987 to the Italian motorcycle maker Cagiva. It turned out that my Husky was actually a Ducati even if it did share quite a few pieces with the original Swedish made 510 four stroke.
The big Husky was quite usable just the way it was, and I had a great time blasting through the tight single track trails that I had always liked to ride. The longer wheelbase and more relaxed steering geometry took some getting used to and the front suspension felt extremely harsh but the big power was very likeable. The problem with the engine turned out to be the ignition system. At the time I did not know quite what was wrong with the ignition system, but it was giving obvious signs of trouble. The engine was always hard to start and it would overheat badly on the tight trails, these problems might have been attributed just to the large displacement but I knew better. The sure sign that it was an ignition system problem was the fact that it would blow the carburetor off after stalling on a tight trail. It was a very annoying procedure to have to disassemble the bike and reinstall the carburetor every time I stalled the engine in the tight technical going.
Being busy with work and having little in the way of access to tools where I was living in town I did little with the Husky other than attend to the trashed chassis by replacing the wheel bearings, brake pads, chain and sprockets and lubing the head set and control cables. Having no flywheel puller I could not check the timing setting, but from reading the owners service manual I got the impression that the ignition system was not really adjustable in any way.
My solution to the overheating on tight trails was to buy a 16 tooth front counter sprocket and a giant 10 paddle sand tire and head to the dunes. As strange as it sounds this was in fact a successful diagnostic strategy. After 30 seconds in the dunes I could tell that the oil reed valve had failed as the engine sounded like it was going to seize up. After it cooled down it restarted and ran as it had before, but again 30 seconds accelerating in the sand and it was in danger of seizing up. The owners service manual said that a special puller was required to get the gears out to check or replace the oil reed valve, so I gave up for the time being and went to live in Germany and study German.
While I was gone my father found that the owners service manual was in error, and the oil reed valve replacement was a simple if somewhat laborious operation. He rode the bike a few times, but it was too hard to start for him. When I got back a year later I once again rode the big Husky, and it was obvious that the kaput oil reed valve had indeed been causing the overheating. The engine still sounded like it had an ignition system problem, but at least it no longer got so hot on trail rides that it blew the carburetor off. The good times did not however last, and the ignition system soon totally failed.
The big Husky had usually been very hard to start, but I was always able to get it going. Then it became nearly impossible to kick start, and would only fire off by rolling it down a large hill. A new spark plug helped, but only very slightly and pretty soon even a brand new spark plug would not get the engine to fire. I even tried towing the bike with a car. One time I was able to get it started this way, but several other times it would not even fire with the engine speed brought all the way up to 4,000RPM.
There was still a visible blue spark when kicking the bike over with the spark plug removed, but the bike would not start on gasoline or starting fluid. Thinking that something might be done about fixing the ignition system I sought out a small shop that at one time sold parts for and worked on Husqvarna dirt bikes. The owner of the shop said that he no longer did anything with the old Husqvarnas and was not at all interested in trying to get ignition parts for me. What he did do though was sell me his old Husqvarna flywheel puller for $20 so that he would really well and truly be out of the Husqvarna business.
I pulled the flywheel off with great difficulty and copious amounts of high pressure grease on the puller threads and found that nobody had been in there in a really long time. With more great difficulty I got the ignition stator hold down bolts out, and played with the static timing setting in both directions. Nothing would get the engine to start.
The cranking compression had always seemed a bit low for a 577cc engine, so I tore the top end down to see what I could find. The piston, cylinder and rings were worn, but not badly. The out of round and taper of the cylinder were still well within what would be considered serviceable even for a race engine and the piston was only slightly worn. The single compression ring did however have an excessive end gap, so I endeavored to replace the rings. The valve guides were also a bit loose, so I wanted to replace them as well. What stopped the project was when I found that although parts were sort of available the prices were not reasonable. The head gasket was $100, the compression ring was $100, the oil control ring was also very expensive and the total with the new valve guides was going to come to $500. This was just plain highway robbery and I would not stand for it.
As the parts looked perfectly serviceable aside from the excessively wide compression ring end gap I just lapped the valves in and put the engine back together. The bike started right up on the first kick and ran as it always had. The next day it again would not start, even when towed up to 4,000RPM with a car. While I had the bike apart I had stored the entire ignition system inside by the fire place, and I got the idea that this had something to do with the fact that the engine had then fired right up.
I took the ignition stator off again and kept it inside by the fire place for another two weeks. At the end of this two weeks the bike fired right up on the first kick and ran as it always had. Again though it would not start the next day. This was then the conclusive evidence of the defectiveness of the ignition system.
I sent the whole ignition system to Ricky Stator in Southern California as they advertised that they could repair all dirt bike ignition systems. I got the ignition system back with a note saying that it was unrepairable, and Ricky Stator had even covered the return shipping at their cost. The local Husqvarna dealer said that ignition parts for those bikes were not available new, and that the going price for a used stator if one could be found was about $500. This pissed me off to no end, but once again all I could do was give up on the bike and focus on other things going on in my life.
Another year later I bought a very trashed looking old 1980 Kawasaki KZ440 sport bike with the front brake system missing. Without the front brake, tachometer cable or serviceable tires and chain the owner was willing to take $500 for the old bike that ran but was hard to start. Hard starting was however relative, and the electric start Kawi would fire up with just the right choke operation. The more I rode the old Kawasaki the easier it started, and I got the impression that the air cooled motor had just been run so extremely hard that the ring seal had suffered. The bald hard compound tires turned out to be so inadequate in the dirt that by the time I got around to buying new tires I also needed new turn signal lenses from crashing so much in the dirt driveway. The 18 inch street tires were extremely inexpensive by motor cycle tire standards, and the new softer compound highway ribbed tires I got were so good off-road that I got in the habit of taking the old sport bike down all sorts of mild dirt trails. The low pipes and extremely high weight of the sport bike severely limited off road potential, and the lack of adjustability of the rear shocks meant that excessive rebound damping caused packing up of the suspension over rocky terrain. On smooth trails though the old sport bike worked fairly well and the motor ran pretty well between 3,000 and 7,000RPM delivering as good as 70mpg over a wide range of operating conditions.
The Kawasaki was however no Husqvarna, and I longed for my old dirt bike back. Interestingly though it was the Kawasaki that gave me the idea of how to fix the Husqvarna. The old Kawasaki used a traditional points, coil and condenser ignition system where the points ran directly on the end of the crankshaft. With the stock ignition system removed from the Husqvarna there was ample room under the side cover for a new ignition system, all I needed was an eccentric for the points follower to ride on.
The $500 that could have gone to new rings or a used stator if one could have been found instead went to buying a new Chinese lathe and milling multi machine that we mounted on the workbench. The cheap but very heavy early Chinese machine tool is clunky and has no lead screw for threading but it has been useful for turning out some custom parts.
Getting a centrifical advance mechanism to work on the crankshaft of an 8,000RPM engine seemed like a difficult task, so I decided not to try to copy the Kawasaki ignition system. Instead I designed and built my own points ignition system. I thought I was going to need some form of advance mechanism at least to get the engine started so I used a points set and advance plate from a 1968 Dodge distributor. Instead of trying to build a centrifical advance I just hooked a cable and spring up to the advance plate thinking that I could use a starting and idling leaver on the handlebars. As it turned out though it was getting the timing perfectly set to one value that was of critical importance and I ended up scrapping the cable and spring system after the first test ride.
I had thought that nearly all gasoline engines used some form of advance mechanism, and I was expecting difficulty in getting the engine to run over a wide range of engine speeds. I did however have some clues that just one fixed spark timing value could be made to work. Generator, pump and small utility gasoline engines usually had just one spark timing value even if they ran over a range of engine speeds, and automotive centrifical advance mechanisms typically topped out at 3,000 or 3,500RPM even if the engine was capable of making power up to five six or even seven grand. The 1980 Kawasaki KZ440 that was my model also had a centrifical advance that topped out at just 3,300RPM despite the fact that it would make power all the way up to 9,000RPM.
Since the big 577cc Husqvarna 610 was so much displacement for a trail bike I was thinking that I would aim for a lower engine speed range. The stock timing setting was 33 degrees BTDC according to the Husqvarna owners service manual, and this had been good up to some unknown but rather high engine speed around 7,000 or 8,000RPM. I decided to go for a normal cruising engine speed down around 3,000 to 4,000RPM and initially set the spark timing on my new points ignition system at 25 degrees BTDC with the cable and spring pulling the timing back to about 15 degrees BTDC for starting and idling.
The bike fired right up on the first kick and ran better than it ever had before. What I quickly found though was that I could not get the timing to stay set well with my cable and spring advance mechanism. The shallow angle on the ignition cam I ground on the lathe meant that small movements of the points caused large changes in the spark timing value. When I watched the spark timing with a strobe light the timing was jumping all over the place. I rode the bike once with the cable advance, but I found that it would only make power in the maximum advance setting, and just the slightest tug of the cable even down at 3,000RPM caused the engine to totally loose power.
Somewhat recklessly I decided to give the engine a kick with the timing at 25 degrees BTDC, and amazingly it fired up even more crisply than it had before. This settled it, the advance mechanism had to go. Once I locked the advance plate down I was able to get a steady timing reading with the strobe light, and this I was very happy about. The bike seemed to run really amazingly well at 25 degrees BTDC, but when I tried backing off to just 23 degrees BTDC I was pleasantly surprised to find just as much maximum power output with much smoother and quieter operation down at low engine speeds. What was surprising was that right in the middle of the engine speed range at 4,000 to 6,000RPM the engine actually seemed to be making substantially more power than it had with the stock ignition system. I then backed all the way off to 19 degrees BTDC but the engine would not make any power at all, not even down at 3,000RPM. I found that the engine would run and make power at 21 degrees also, but I thought that going just two degrees more would probably be a good idea since the stock setting was supposedly way up at 33 degrees BTDC. The bike seemed to be a bit crisper and perhaps run a bit better with a static timing setting of 23 degrees BTDC so I chose this as my initial running setting. I also found that there was nearly perfect agreement between the static timing setting using a test light and the observed spark timing using a stroboscopic timing light. One strange thing that I noticed when revving the bike with the timing light hooked up was that my otherwise rock solid spark timing setting began to jump around very slightly up at high engine speed. The instability of the spark timing appeared to be only a few degrees of crankshaft rotation so I just wrote it off as some anomaly and ignored it for the time being.
As I rode the bike a bit I was astounded at how much more power it was appearing to put down than it ever had with the stock ignition. What was really the most surprising was that even with a spark timing of just 23 degrees BTDC there seemed to be no limit to how high the engine would rev, it just kept going and going and making more and more power. I put an automotive tach on the handlebars for a test ride, and although the needle was jumping around a whole lot at low engine speeds it leveled off and read accurately above about 4,000RPM. I was amazed to see that the engine would rev to 7,000RPM with a moderate throttle opening and would rev even higher wide open. It was a bit difficult to watch the tach while laying down full power output though, and I just called it a 7,000RPM maximum for most purposes.
As well as the points ignition system worked for laying down big power it was not without difficulties. One very significant problem was that I had no onboard charging source, meaning that the Husky had become a battery operated toy. At first I had trouble with motorcycle starting batteries failing, and twice I had to walk home when the battery unexpectedly went dead on me. When I switched to sealed AGM lead acid storage batteries the unexpected failures were eliminated, but I still had difficulty with figuring out how to charge the batteries. When I bought my first 5Ahr 12V AGM battery at a local dealer I enquired about a charger for it and was offered an unregulated "wall wart" transformer and rectifier with clips on it for $25. Somewhat offended by not being able to buy a regulated charger I just used an unregulated 12V wall wart that I already had laying around. I knew that the sealed battery could easily be destroyed by overcharging with an unregulated charging source, so I tried hard to disconnect the charger as soon as I had put a substantial amount of charge back in the battery. This worked for a while, but my first two 5Ahr AGM lead acid batteries died after just a few months of not coming up to a full state of charge. The next two 4.5Ahr AGM lead acid batteries I used were a very cheap model from a mail order company, and I decided that they needed more charging. These new cheaper and lighter 4.5Ahr AGM batteries I always tried to charge up to over 14V, but it was tricky and difficult to catch the charger at just the right time. If I left the 0.8A charger go for too long the voltage quickly would climb up to over 15V. In the first half a year or so I was very careful to always catch the charger at about 14 to 14.3V and the batteries held up to substantial use and many dozens of cycles. Then I got sloppy and both batteries were forgotten for long hours several times. The batteries still worked after this abuse, but the capacity dropped off to the point where I once again needed new batteries.
The last set of batteries I ordered were also very inexpensive and rated at 5Ahr in those same small cases. This time I also sought out a voltage regulated charger and this last set of batteries lasted for many years of substantial use.
At first the points ignition system used quite a lot of power with the 1960's Dodge coil and a ballast resistor. Because the lead acid batteries were so heavy I tried to get the current consumption of the ignition system down. What I found was that I could use a later model 12V coil labeled as not requiring a ballast resistor with or without the two ohm ballast resistor. Without the ballast resistor the late model coil used just about as much average current as the old coil with the two ohm ballast resistor. When I added the two ohm ballast resistor in line with the late model coil the bike still made just as much power and revved just as high while drawing substantially less electrical power. With this modified ignition system I was able to get a whole tank of gas on one 5Ahr battery, and there was the added benefit of the bike losing power at the very end when the battery voltage dropped down bellow about 11V. I still always carried a second battery though as I never quite knew when one was going to give up the ghost for good.
These two 5Ahr 12V lead acid batteries weighed in at about ten pounds and severely compromised the handling of the bike being located in a fender bag on the rear fender. Several times I tried mounting a motorcycle starting battery directly to the inside of the rear fender behind the shock absorber to move some of the weight forward and down, but they always failed within just a few weeks. What did finally get the weight down a bit was the use of a little 3Ahr 12V nickel metal hydride battery pack I made up out of AA size cells. This little pack would also go for a whole tank of fuel, but weighed a whole lot less than the a 5Ahr lead acid battery. Since the little AA size Ni-MH cells were so expensive at that time I still used a 5Ahr AGM lead acid battery for normal ridding and always carried the Ni-MH in reserve but rarely cycled it.
The other big problem I had with the points ignition was that the fixed spark timing sometimes caused the bike to kick back when starting it. This ruined a whole lot of pairs of boots and shoes and made ridding the bike frustrating sometimes. The timing setting was extremely critical for preventing kicking back. At a static timing setting of 25 degrees BTDC the 610 kicked back so severely that it was almost impossible to start. At a static timing setting of 23 degrees BTDC it made just as much power but only occasionally kicked back. Down at a static timing setting of 21 degrees BTDC the 610 essentially never kicked back and was very easy to start. The problem with the 21 degree BTDC static timing setting was that the engine hesitated up at higher elevations. At sea level it ran clean and made big power instantly, but up at 5,000RPM there was a bit of lag at around 4,000 to 5,000RPM when the throttle was first cracked open. This hesitation was annoying, but I found that I could still deliver full power with the 21 degree BTDC static timing setting by rolling the throttle on just right through the midrange before opening wide for full power up at 6,000 to 8,000RPM. I liked the way the bike ran up at a static timing setting of 23 degrees BTDC much better, and I ran it like that much of the time I rode it. For a while though when I was using the 610 around town down at sea level I left the static timing setting down at 21 degrees BTDC so that I could get it started without ruining street shoes.
I had my beloved 1991 WMX 610 to use for quite a few years, and I rode it a lot in that time. I also took advantage of having an onboard battery to meet the California headlight on without the engine running requirement and got a license plate for the four stroke motorcross bike. It was a fun and easy project putting all of the lights and other equipment on the Husky to get the license plate, but those lights did not end up working out all that well. The biggest problem was the rear turn signals getting damaged in trail ridding. The front stalk type turn signals easily mounted the sides of the headlight plastic and tucked nicely up inside the radiator shrouds when the bars were turned all the way to the side. The rear turn signals though just stuck out in the middle of nowhere. I chose flush mounted turn signals that were barely useful for signaling, but they still ended up broken when I dumped the bike over on tight tails.
It was easy to power the turn signals and brake light off of the little battery as the 1.7A bulbs were not on for long periods of time. The 25W high and low beam headlight was however too much for the little lead acid batteries. Not only did the two amp draw suck down the batteries quickly, but the combined draw of the two amp headlight, half amp taillight and the one amp brake light in addition to the ignition draw meant that the engine began to lose power when the battery was only about halfway discharged. The result was that the headlight was useful for short emergency trips at night, but any kind of long distance night ridding was absolutely out of the question.
Gearing had always been a problem on the WMX 610, as the five speed transmission always seemed to be missing either first or sixth gear. The stock gearing of 52/12 worked well for trail ridding, but was in fact so low that the jumps between the higher gears seemed too narrow. Going up to 52/13 gearing worked much better for most purposes, but there were of course times when first gear did not seem quite low enough for comfortably negotiating tight turns on small single track trails. The 52/13 gearing was also not quite high enough for highway use. To cruise at a reasonable engine speed on the highway the 51/14 gearing I often used was much better, both allowing higher sustained cruising speeds and less shifting on small twisty paved roads. With the 51/14 gearing tight technical single track trails were however much more difficult, requiring copious use of the clutch and bringing back not altogether fond memories of clutch slipping on the CR 125.
The requirement of DOT approved tires was not a problem as I had already been using Kenda K760 Track Master II tires for quite a few years on all of my green sticker dirt bikes. I liked the Kendas first and foremost because they were very inexpensive, but they also had just a really pleasant and controllable manor to them while also hooking up good enough to hold their own against the best motor cross tires. On the highway it is easy to wrack up considerable miles though, and I often sought out longer lasting dual sport tires. The Pirelli MT 21s were the long life king and they worked fairly well under all conditions. Maximum drive, braking and cornering traction on trails was however not as good as with the Kendas. I also liked the Dunlop D606 dual sport tire because it was also very long lasting and had good drive traction in the dirt. The downsides of the Dunlop were that it was very expensive at the time, did not corner as well as the Kendas and tended to tear trails up worse than anything else in existence. What I decided was that the Kendas were the best dual sport tires, and highway ridding was just very expensive on a dirt bike.
The requirement of a quiet exhaust system for street use was something that I had already taken care of years before as well. The small stock muffler on the WMX 610 was loud beyond all reason. It hurt my ears with a helmet on, and I was told that I could be heard coming five miles away. The bike had come with a partial custom exhaust system for using a Supper Trap brand diffuser disk type muffler, but this did not work any better. With the full 11 disk stack the muffler was just as loud as the stock motorcross muffler. Removing just a few disks did not quiet the exhaust down at all, and it was not until nearly half of the disks were removed that the exhaust got quieter. With enough disks removed the exhaust certainly was substantially quieted, but this also hurt performance considerably. The bike just made a lot less power choked off so much.
I got the idea for the solution from a drawing in the 1991 Husqvarna owner’s manual which showed two inline mufflers on a European enduro version. The small forward muffler looked the same as the stock muffler I had, but a second muffler was mounted back by the rear fender. I stuck my Supper Trap muffler on behind the stock muffler with a custom mounting bracket and the sound problem was solved. This dual inline muffler system quieted the bike down a huge amount without hurting performance in the slightest. The bike became so quite that it was in fact one of the quietest street bikes around. Only way up at the top of the engine speed range wide open at 8,000RPM did it still make a large amount of sound, and even this was a whole lot less than it had made before.
The big 577cc Husqvarna motor was able to do amazingly well on fuel out on the open highway, turning in 50mpg on anything from a big fast dirt road to a 70mph freeway cruise and high speed performance was quite good. With high enough gearing it would easily pull up to over 100mph on the beach and never seemed to lack power under any circumstances. For my favorite type of riding on tight trails the big 610 was however still somewhat of a fuel hog. It certainly went a lot further than my old 125 two stroke, but this was due to the larger 2.4 gallon tank and the fact that the mileage spiked up on connecting sections of faster dirt roads and bigger trails. On the tight trails it still only got the same 25mpg that the 125 two stroke had.
Then in 2005 while I was working on the Norsea 27 refit project my trusty old Husky died. The cranking pressure had been falling off for a while, but then all of a sudden there was just no compression when pushing the kick starter down. I could still get the engine started, but it took a monumentally huge kick and I knew that something was seriously wrong. I had put only about 300 hours on it since getting it running with the points ignition system, but this was considered quite a bit of engine run time for a dirt bike.
I had always felt that the size, weight and power of the 1991 WMX 610 were excessive. It was a fast bike that could do amazing things, but it was still pretty heavy at 272 pounds ready to ride with a full tank of fuel and really more power than a dirt bike required. In light of the arguably excessive amount of power that the 610 was capable of making I had long been interested in the smaller Husqvarna 350 that I read about in the 1991 Husqvarna Owner's Service Manual. The 350 was however not lighter. It was in the same engine cases as the 610 with the same clutch and transmission and used the same chassis. I was still interested in the 350 though, and when I was able to buy a 1992 Husqvarna 350 enduro model with a license plate already on it for $1600 I jumped on the chance.
The 1992 TE 350 looked just like my 1991 WMX 610, but it had the six speed transmission I had so coveted and it had different suspension on it. I did not think much of the forks being 43mm Showas instead of the 40mm White Power units I had on the 1991, but this did turn out to be a significant difference. The 1992 TE 350 was running on the stock ignition system, and seemed to have less of the excess harshness that the 610 had on the stock ignition system. The only thing that was immediately wrong with the 1992 TE 350 was that the water pump impeller hold down screw was broken off and the impeller had worn itself out against the pump housing to the point that it no longer worked. I had not detected this problem on the short test ride, and I likewise had not detected any problem with the suspension on that short test ride up a smooth paved street.
The water pump was easy enough to fix by gluing the impeller in place close enough to the housing for it to pump. At first I had a bit of trouble with some crappy epoxy I was getting softening too easily in boiling water, but eventually I was able to get normal epoxy that held up to boiling water just fine. I never had a failure of the water pump on the bike, but I had to take it apart and put a different brand of epoxy on when I only thought to do the boiling water test after I had already re-assembled the bike.
At first the 1992 TE 350 did not rev out very well, and power output was only mediocre. On my first long test ride I used up most of the fuel that had been in the tank and filled up at a gas station with premium. On the new fuel the little 350 engine really came alive, and made absolutely huge amounts of power up to 10,000RPM. The good times did not however last, and one day while passing two trucks on the highway that were going slow in the twisties and then quite fast on the straight section with a passing lane the rod bearing failed. Just a few miles later the engine seized up and I again found myself walking.
On the KZ440 I had learned that it was not a good idea to follow vehicles on the highway, and that passing was best done as soon as possible. On the new 350 with the Japanese suspension I was however a bit reluctant to ride aggressively in traffic not being familiar with the bike. Instead of passing with lane sharing as is normally considered best practice on a motorcycle I had waited for the straight away with a passing lane to have lots of room to work with. That was the end of the short but illustrious life of the stock 350 motor.
The high engine speed failure of the little 2.48 inch stroke motor was not so much a failing of the engine itself as it was a failing of the oil reed valve lubricating system. Without pressurized oil fed directly into the rod bearing the engine is just not able to hold up to sustained extremely high engine speeds. On the big three inch stroke 610 motor the same lubricating system weakness exists, but the larger motor neither has to rev as high or stay at that high engine speed for as long. The fact that the rod bearing is a quarter inch farther away from the oil squirter on the short stroke engine also probably has something to do with it's much higher propensity for failing at sustained high engine speeds.
As a stock replacement rod kit was not available for the 350 motor I had to get creative to effect a repair. Spurred by the suggestion from Crankworks in Tempe, Arizona that perhaps some other connecting rod could be made to fit I designed a repair using a Honda XR 400 connecting rod. Since the XR400 rod is somewhat shorter at 122.6mm than the stock 127mm Husqvarna rod some other adjustments were required to get the compression ratio to come out. A high compression piston for an XR 400 from Wiseco helped a bit with it's small pop up dome, and removing the base gasket lowered the cylinder head 0.020" without making the timing chain so excessively long as to not be well tensioned by the spring loaded tensioner. These small shifts towards a higher compression ratio would however still have yielded an excessively low compression ratio compared to the stock 10.2:1 compression ratio. To get the compression ratio to come out close to stock I had Crankworks move the crank pin out 0.010" to set the stroke at 2.68 inches.
The top end on the 1992 TE 350 was pretty well trashed. The cylinder did not have any tapper or out of round, but it had been honed out to where there was 0.009" of skirt clearance on the piston, way too much for most any normally aspirated race engine. I had the cylinder bored 1mm oversize to take the 85mm XR400 piston, and I requested the high end of the Husqvarna 350 stock skirt clearance range of 0.0027 to 0.0036 inches. I sent U.S. Chrome in Wisconsin the piston with the cylinder, and they hit my requested skirt clearance right on with 0.0034 inches. The Wiseco piston with its small oil retaining ribs also tends to work like it has a bit more skirt clearance than it actually does both because the ribs retain oil well and also because the tops of the ribs wear away quickly and increase the skirt clearance. Even in the air cooled XR 400 Wiseco recommends only about 0.0025 inches of skirt clearance which is still enough to work quite well for a three inch forged piston.
The intake valves were also in very poor condition on the 1992 350 with it's extremely fast closing intake ramps. Essentially the 1992 roller cam is so aggressive that the intake valves just float and drop at the highest engine speed. This is good for performance, but causes the intake valves to crash into their seats at high engine speed. This had caused small cracks to develop on the intake valves, and leaking exhaust gas was cutting it's way through the valves once these cracks started to develop.
Sticking with the Japanese style parts for the repair I found that Mazda Miata valves were nearly identical to the original Husqvarna valves. Somewhat ironically the nice black coated valves I ordered from the local auto parts store for only $8 a piece turned out to have been manufactured in Italy.
When I got the crankshaft back from Crankworks I was very disappointed to find that the radial clearance on the rod bearing was only about 0.0002 or perhaps 0.0003 inches even after I washed all the oil out of it with solvent. This did not seem like enough oil clearance since the stock Husqvarna specification was 0.0011 to 0.0014 inches. I complained to Crankworks about the tight clearance, but was told they have put many two strokes together with that tight of oil clearance. As there was a bit of taper to the bearing race, meaning that the tightest clearance was only in the middle with some unknown wider clearance at the edges, I thought there might be a chance that it would somewhat work.
The new engine ran great when I got it back together, but once again the good times did not last. Just ten miles up the trail on my first test ride the transmission jammed in two gears and broke a bunch of gear teeth off of fifth gear on the auxiliary shaft and fifth and sixth gears on the main shaft. I swear someone moved that shim from the outside of third gear on the main shaft to the inside of the gear when I was not looking. Not knowing of anywhere to get replacement gears I gave up on the project and began looking for something else to ride.
The trusty old Kawasaki KZ440 was not much fun after the Husqvarnas and did not even make as much power as the 350. The KZ440 acctually did pull pretty hard from 6,500 to 8,000RPM, but this was too narrow of an engine speed range for off road ridding. Despite the large displacement power was weak bellow 6,000RPM and despite the short 2.44 inch stroke the engine did not work all that well at the highest engine speeds. The heavy rod bolts, two valves per cylinder and an only very slightly oversquare configuration meant that the engine sounded loud and loose above 8,000RPM and power dropped off towards the 9,000RPM maximum engine speed. The Kawi did however come to the rescue by catching the fancy of a young guy who's 1991 Husqvarna WXE 350 had stopped running on him. The Kawi was old and slow, but it did run sweet and we traded straight across one running cow for a dead Husky. I am not sure who got the better deal, but we were both extremely happy to be rid of our dead horses.
I could not get the WXE 350 to start by changing the timing, and it appeared that the stock Swedish made SEM ignition system had failed like the one on my WMX 610 had. I just ripped the points ignition off of the dead 610 and put it on the 350 and was up and running in nothing flat.
Since I always ran the 3.86 inch bore Husqvarna 610 at a static timing value of 21 or 23 degrees BTDC I figured that the 3.31 inch bore Husqvarna 350 with the same 10.2:1 compression ratio would require a static timing value of about 18 degrees BTDC. When I first fired the WXE 350 up at 18 degrees BTDC it did run quite well, but there was a huge amount of hesitation which severely interfered with power delivery. Going up to a static timing setting of 23 degrees BTDC got it running great, but it did not stay that way.
Every time I bought fuel it was different. I was having to change the static timing setting on each fuel up, and the timing settings I was having to run were all over the board. Sometimes it ran great with a static timing setting of 23 degrees BTDC, and other times I had to go up to 27 degrees BTDC to get it to run at all at higher elevations. At one point I was all the way up at 36 degrees on the static timing setting and when I fueled up at a gas station the bike ran really harsh and made much less power. I changed the static timing setting down to 27 degrees BTDC and it ran great. I even went all the way back down to 23 degrees on that tank, and it was running pretty well below 3,000 feet of elevation but would hesitate up at 5,000 feet.
It went like this for the whole year that I rode the stock 1991 WXE 350, although there was a period of several months where the bike ran the same all the time with a static timing setting of 33 degrees BTDC. I always wanted to get the static timing setting down to the least amount of advance that I could as the large amounts of spark lead caused harsher operation and hurt maximum power production quite a bit also. Especially down at 3,000 to 5,000RPM the large amounts of spark lead caused torque production to suffer significantly. Interestingly the premium grade 91 (RON+MON)/2 octane rating gasoline that I always ran usually seemed to have a rather high flame front travel speed, and the engine sometimes would still make quite a bit of power as it hesitated horribly up at 5,000 to 7,000RPM. Sometimes on the fastest flame front travel speed fuel the engine would hesitate at 4,500 to 5,500RPM but then make big power all the way up to over 8,000RPM, and other times on slightly slower flame front travel speed fuel the engine would run well enough through the midrange and then hesitate horribly up at 7,000RPM and up.
The stock 1991 WXE 350 ran better than the stock 1992 TE 350, making more power from 3,000RPM to 6,000RPM. The 1992 TE 350 with the stock ignition system had been pretty weak bellow 6,000RPM, and then it came alive for a brisk pull from 6,000 to 9,000RPM. The otherwise stock 1991 WXE 350 with the points ignition system pulled much harder from 3,000 to 6,000RPM even when the fuel was requiring a static timing setting of 33 degrees BTDC. The 1991 WXE 350 also made more power up at 8,000 to 10,000RPM, although this was somewhat inconsistent as the fuel radically changed from week to week. I attributed the abrupt power hit on the 1992 TE 350 to the somewhat different exhaust system which uses larger diameter header pipes and also dumps the two header pipes into the one larger pipe closer to the engine than on the 1991 exhaust system.
When the rod bearing finally failed after I had put 135 hours on the stock 1991 WXE 350 I blamed a mismatch between the fuel and the compression ratio of the engine for the failure. It was the fuel for 13:1 and 14:1 engines that was requiring so much spark lead and hurting maximum torque production from 4,000 to 6,000RPM. With maximum torque low at less than 6,000RPM I was having to rev the engine up to 8,000 and even 10,000RPM all the time to get the power that I otherwise could get down at 5,000 to 7,000RPM. I was, after having destroyed the 1992 TE 350 on the highway, very aware of the limitations of the oiling system on the early Husqvarnas, and I always tried to prevent the engine speed from staying up at high levels for long periods of time. Just revving to 9,000 or 10,000RPM for a second or two to get into the next gear did not appear to do much damage to the rod bearing as it stayed somewhat lubricated just from the oil that was already in it. In the last months that I rode the stock 1991 WXE 350 the fuel jumped back and forth so that sometimes I was able to run 33 degrees BTDC on the static timing setting but much of the time I had to run 35 degrees on the static timing setting to get the engine to run well.
The failure of the rod bearing on the stock 1991 WXE 350 caused metal shavings to come out with the drain oil and the engine became very loud and loose. Over just a few hours this looseness got much worse but the engine did not seize up. When I tore the toasted engine apart I found that the rod bearing had 0.006" of radial play in it, so much that it clanked around when moved by hand even with oil in it. When I washed the oil out of the rod bearing with solvent it felt even looser.
This time I had all the parts I needed to effect a repair, and I had the 1991 WXE 350 up and running with the new 386 stroker motor in just four days after I first tore it down. The most interesting thing I found when tearing both the 1992 TE 350 and the 1991 WXE 350 engines down was that they did not have the same camshaft in them. The 1992 cam was about 260 degrees at 1mm valve lift, where the 1991 cam was only about 245 degrees at 1mm valve lift. Both cams are big aggressive roller cams that keep the valves nearly full open for over 120 degrees of crankshaft rotation. As it turns out the 1991 cam is big enough for the 10,000RPM 350 engine, and the even bigger 1992 cam is excessive to the point of hurting engine performance a bit down at the bottom of the engine speed range around 3,000 to 4,000RPM. The secret of the success of the 1991 Husqvarna is the aggressive fast opening and closing valves on the rollerized valve train. Just 245 degrees of duration at 1mm valve lift is enough if the valves can be opened and closed fast enough that they stay substantially open for a long period of time.
When I put the 386 stroker motor together I used the 1992 cases that the crankshaft was already installed in, but I dropped the whole 1991 six speed transmission in. I also used the 1991 camshaft and the 1991 clutch.
The result is a very good running Husqvarna that pulls very hard all the way from 3,000RPM up to over 8,000RPM. The longer stroke tends to limit maximum engine speed, but the Pro-X brand XR400 rod is actually quite a bit lighter than the original Husqvarna rod making for amazingly good high engine speed performance. I also cut the Wiseco piston down to where it is an ounce lighter than the stock Husqvarna piston despite it's full XR style skirts and long piston pin.
The compression ratio of the new engine came out to about 9.8:1, but amazingly I have been running from 23 to 27 degrees BTDC on the static timing setting with excellent results. The combination of the 11% increase in displacement and a 8% increase in stroke add up to some inevitable increase in torque production. With fuel that runs down at a spark timing value of 23 degrees BTDC though the increase in torque production is quite dramatic, making the 386 stroker motor an excellent solution to the oil reed valve oiling system. Being worried about the overly tight Pro-X brand rod bearing I tried to break the new engine in down at low engine speeds of less than 5,000RPM. At first I got some metal shavings out with the drain oil, but this subsided after the first few hours of operation. I am not sure if the metal shavings were from the rod bearing or left over gear material from the transmission failure, although I did very thoroughly clean the cases out before reassembling the engine. It seems likely that the tight center part of the Pro-X rod bearing did in fact fail and grind out as metal shavings, but the wider side clearances were able to support the load and allowed the engine to run in. After 20 hours of operation I began to rev the new 386 stroker motor up to 7,000 and 8,000RPM quite a bit, and no more metal shavings have come out.
I first saw the crankshaft wiggle advancing effect on the 1991 WMX 610 shortly after I got it running with the points ignition system in 2002, but it took me many years to figure out just what it was that I had seen. It was when I got the 1991 WXE 350 running on the same points ignition system that I finally figured out just what it was that I had been observing but not recognizing for all those years.
The crankshaft wiggle advance happens because the crankshaft is both forced down by the compression pressure on the piston and is also pulled up on by the rod and piston being flung upward by centrifical force. At low engine speed the compression pressure on the piston keeps the crankshaft forced down on the main bearings and the engine runs at a spark advance value equal to the static timings setting. At some higher engine speed the centrifical force of the piston and rod being thrown up as the engine approaches top dead center overcomes the compression pressure on the piston and the crankshaft is forced upwards to the other side of the main bearings. This crankshaft wiggle advance comes all at once at one engine speed. The engine speed at which the crankshaft wiggle advance comes at is determined by six things: The weight of the piston and rod, the bore size of the engine, the compression ratio of the engine, the volumetric efficiency of the engine and the stroke of the engine.
It is easy to see that a lighter piston and rod will cause the crankshaft wiggle advance to come at a higher engine speed because the lighter parts will not be pulling up so hard on the crankshaft. The stroke of the engine is significant because a longer stroke throws the piston and rod up faster, causing the crankshaft wiggle advance to come at a lower engine speed. Said a different way the crankshaft wiggle advance would tend to come at the same mean piston speed for engines of any stroke. An engine of four inches of stroke would tend to have the crankshaft wiggle advance come at 4,000RPM and all else being equal an engine of two inches of stroke would tend to have the crankshaft wiggle advance come at 8,000RPM. It is also easy to see that a higher compression ratio would tend to cause the crankshaft wiggle advance to come at a higher engine speed just because there is more pressure on the piston to counter the force of the piston and rod being thrown up by centrifical force.
The last factor in the engine speed at which the crankshaft wiggle advance comes turns out to be of paramount importance because of the ramifications it has for the way the engine runs over a range of engine loads. Higher volumetric efficiency gets more intake air into the cylinder and increases the compressive pressure on the piston, in turn causing the crankshaft wiggle advance to come at a higher engine speed. What is so significant about this is that by closing the throttle slightly the volumetric efficiency is reduced and the crankshaft wiggle advance then tends to come at a lower engine speed. This then is the poor man's throttle position sensor, opening the throttle causes the crankshaft wiggle advance to come at a higher engine speed which has the effect of reducing harshness under a heavy load. This volumetric efficiency dependency of the engine speed at which the crankshaft wiggle advance comes is a rather small effect, but it is significant and tends to get a single cylinder engine with the points running on top of the crankshaft to run somewhat better over a wide range of speeds and loads than could be obtained with a truly fixed spark timing value.
The only things that determine the amount of crankshaft wiggle advance that is obtained are the steepness of the ramp on the ignition cam where the points open and the amount of play in the main bearings. A steeper ramp where the points open causes a smaller amount of crankshaft wiggle advance because the wiggle in the main bearings then represents a smaller number of degrees of crankshaft rotation along the ignition cam. Likewise a shallower angle on the ignition cam where the points open causes a larger amount of crankshaft wiggle advance. Obviously more play in the main bearings causes more crankshaft wiggle advance and less play in the main bearings causes less crankshaft wiggle advance.
The crankshaft wiggle advance is undeniably useful for getting a single cylinder gasoline engine to run better over a wider range of engine speeds and loads, but it's utility is still extremely limited. The big problem with the crankshaft wiggle advance is that it is an all at once advancing effect, which means that there tends to be some choppiness in the power delivery if the engine is not tuned just right. Because the crankshaft wiggle advance tends to come up at a fairly high mean piston speed this choppiness does not however typically interfere with smooth power delivery in tricky maneuvering situations where small amounts of power are used.
The crankshaft wiggle advance can really only be used on single cylinder engines, but some crankshaft wiggle advance may be observed under some circumstances on inline twin and inline four cylinder engines as well if the points are run directly on the crankshaft. On inline twin and inline four cylinder engines the other rods and pistons forcing the crankshaft downward tends to make the crankshaft wiggle advance come at such high mean pistons speeds that it would be totally useless for most normal high performance engines.
When I put the 386 stroker motor in the 1991 WXE 350 with the points ignition system I expected the reduced rod and piston mass to cause the crankshaft wiggle advance to come at a higher engine speed. On the stock 1991 WMX 610 and the stock 1991 WXE 350 the crankshaft wiggle advance had come at about 5,500RPM under a full load, and part throttle operation caused the crankshaft wiggle advance to come at slightly lower engine speeds. Particularly on the 1991 WMX 610 the crankshaft wiggle advance sometimes appeared to come at significantly lower engines speeds down to perhaps 4,500RPM with the throttle partially closed. This was the reason that with a static timing setting of 21 degrees BTDC up at 5,000 feet of elevation I found that I needed to roll the throttle on just right to get the 610 motor to run clean without hesitation. On the stock 1991 WXE 350 the crankshaft wiggle advance always came very close to 5,500RPM, and the throttle position seemed to only very slightly change the engine speed at which the crankshaft wiggle advance occurred.
As expected the crankshaft wiggle advance came at a somewhat higher engine speed on the new lighter 386 stroker motor despite the slightly longer stroke. Because the new main bearings on the 386 stroker motor were tighter the amount of crankshaft wiggle advance was also smaller. This smaller amount of crankshaft wiggle advance coming at a higher mean piston speed allowed the 386 stroker motor to run smoother and more consistently over a wide range of engine speeds, and there was little in the way of noticeable choppiness from the all at once crankshaft wiggle advancing effect.
With the new 386 stroker motor running well in the 1991 WXE 350 chassis and a perfectly serviceable 1992 Husqvarna chassis sitting in the garage with no motor in it I somehow decided to turn my attention back to my old 610 motor. Not only had the 610 motor lost compression, but the 1991 WMX chassis was not in great shape either. The 1992 chassis on the other hand was all together and ready to go.
The 610 motor had started to get very loose and made horrendous rattling noises at higher engine speed in the last year that I had ridden it back in 2005, and in light of the rod bearing failures I had had on the 350 motors I fully expected to find the rod bearing in the 610 total toasted. Part of the reason that I was motivated to take the 610 motor apart is that rod kits and pistons are now available for the 1991 to 2000 Husqvarna 610 motors. The rod in the 610 has the same 127mm center to center length and the same 38mm big end bore as the rod in the 350 motor, but the 610 uses a larger 22mm piston pin. The 20mm piston pin in the 350 and the 22mm pin in the 610 means that the rods are not interchangeable even though they are essentially identical. This makes the 350 a long rod motor with a rather heavy connecting rod and makes the 610 a short rod motor with a very lightweight minimalistic rod and rod bearing.
When I got the head and cylinder off of the 1991 610 motor I was pleasantly surprised to find that the radial play in the rod bearing was well within the Husqvarna specification. After rinsing the oil out of the rod bearing it looked like it was probably not much more than the 0.0011 to 0.0014 inch standard clearance, and well below the 0.0031 inch wear limit listed in the 1991 Husqvarna Owner's Service manual. What I did find to have extremely excessive radial clearance though was the piston pin. The piston pin itself was worn down by 0.0013 inches and the bronze bushing in the rod was also worn somewhat to bring the total clearance up to nearly 0.003 inches.
The piston and cylinder also turned out to be in very good condition, and looked really just like they had back in the year 2000 when I took the 610 motor apart the last time. For a dirt bike 300 hours is considered a lot of hours, but my 610 motor had worn more like 300 hours on an automotive engine and was still really in excellent condition. It turned out that the loss of compression was just a burned exhaust valve seat, and the stainless steel valves themselves were still in great condition.
To put the 610 motor back together I just lapped in the valves and slapped a new piston pin in. I was not able to get an exact replacement piston pin as the new Woessner brand pistons available for the 610 are of a new design that use a shorter piston pin. What I did instead was to order a 22mm piston pin from Wiseco that was a bit longer and I turned it down to length in the little cheap Chinese lathe. As expected the 4mm wall thickness piston pin was extremely tough, and took a whole lot of tool pressure to cut with a carbide cutter. I was however able to get the pin down to length with the carbide cutter, and I only had to use a grinder to de-burr the corners to make assembly easy.
I had had so much success cutting down the Wiseco XR 400 piston that I decided to take some weight off of the stock WMX 610 piston as well. As it turned out the 610 piston was a lighter design to start with, and finding extraneous material that could be easily removed was much more difficult. I did however find extra material around the pin bosses that was doing nothing but making the piston heavy, and I was able to bring it down from 406g to 366g with an afternoon of drilling and grinding with a hand grinder. The 610 piston is already a rather short skirt design for the big three inch stroke to clear the crankshaft with the short five inch rod, and again I left the skirts fully intact.
Because my original points ignition system was being used on the 386 stroker motor I had to build a whole new system, but this turned out to be quite easy knowing what it was that I was trying to do. The first points ignition system I built back in 2002 was sort of a crude hacked together affair, and it is a miracle that I was able to get it to work at all.
First of all I decided to mount the new points directly on an aluminum backing plate and do away with the old Chrysler distributor advance plate. This made the mounting of the points considerably easier to accomplish, and the stiffer mounting also turned out to be easier to tune and more reliable. The other big difference with the new points ignition system I built was that I cut the ignition cam only partway down, meaning that the points do not open as far. The ramp where the points open is still approximately on the same angle, but the cam then flattens out so that the maximum points lift is only about 0.015" instead of the 0.030" of the original fully round cut ignition cam. The smaller overall opening of the points does not interfere with the operation of the ignition system in any way, but does mean that the cam follower does not wear down as quickly. With a nearly one inch diameter cam over the end of a crankshaft that spins up to quite high speeds cam follower wear was a bit of a problem, although I was able to get just the one set of points to last for hundreds of hours by finely polishing the cam and always running copious amounts of cam follower grease.
The fully assembled 1991 610 motor dropped right into the 1992 chassis and fired up on the first kick as always. This time the fuel was however a bit different. It took a static timing setting of about 26 degrees BTDC to get the engine to run without hesitation but there was no kicking back what so ever. The 350 engines never kicked back on me when starting, and I thought this was because the smaller displacement engine was just easier to spin over with a brisk kick. As it turns out though it is the volatility of the fuel that determines how easily the engine starts and how likely it is to kick back. The new fuel in the resurrected 610 has never kicked back on me even though I have now tried static timing settings everywhere between 21 and 29 degrees BTDC.
The other big difference with the new fuel is that it is much more sensitive to engine temperature changes. Although the 610 motor will now run with as little as a 21 degree BTDC static timing value there is a lot of lag in throttle response down at that late timing value. This lag is not exactly the same as hesitation because it is very time and temperature dependent where the hesitation is just an unwillingness of the fuel to light off on late compression ignition under some speed and load conditions.
On the new fuel the 610 motor tends to run extremely clean and crisply on tight trails where the cooling system heats up. Even with just a 21 or 23 degree BTDC static timing value the 610 was working quite well on tight trails and even out on bigger trails if I was using lots of heavy acceleration and aggressive braking to keep the engine hot. In casual cruising with lots of coasting in high gears though the lag was just too much, and I bumped the timing up to about 25 degrees BTDC where the engine ran crisply and cleanly under all conditions. I have noticed some small changes in the way the 610 runs from batch to batch on the 91 (RON+MON)/2 premium gasoline I have been buying, but the changes have been extremely small.
In order to do a head to head comparison of the small bore 386 stroker motor and the big bore 610 motor I took to ridding one bike for a half hour, then I would drain the fuel into the other bike and ride the same half hour loop. By swapping the same fuel back and forth between the bikes several times I was able to get a good honest comparison of the differences between the two motors. The biggest thing that stands out in this comparison is that the new fuel is a whole lot more engine temperature dependant than any of the fuel that I ran in either the 610 or the 350 motors in the past. On the smaller 386 stroker motor this temperature dependence meant that the engine had to be run extremely hard to bring it up to a high temperature where it would run the same as it did in the 610.
When the 610 was running fairly crisply with no undue hesitation at a static timing setting of 25 degrees BTDC the 386 stroker motor was able to run similarly at about 23 degrees BTDC, but only when it was well warmed up after a few pulls of heavy acceleration. On another day when a different batch of fuel did not have quite so much engine temperature dependence I was running the 610 at 23 degrees BTDC and the 386 was lighting off pretty well all the way down at a static timing setting of 21 degrees BTDC. This is not the 18 degrees on the 3.3 inch bore and 23 degrees on the 3.9 inch bore that I had expected, but it does certainly indicate that bigger bore engines need more advance.
As similar as the 350 and 610 Husqvarna motors are, there are some significant differences. One is that the 34mm DellOrto slide type carburetor on the 350 is not jetted quite as rich in stock form as the 40mm DellOrto on the 610 motor. The slightly richer jetting on the 610 means that it will light off on late compression ignition somewhat more easily than expected. The other significant difference between the two motors I was running is the fact that the 386 stroker motor is a bit light on compression ratio compared to the stock 350 motor. The stock compression ratio of both the 610 and the 350 is 10.2:1, but my Honda rod and piston equipped 386 stroker motor came out just a bit lower at about 9.8:1. The less than half a point difference in compression ratios is small, but still quite significant.
The 1992 chassis that I had not liked with the stock 350 motor in it turned out to be a different animal with the more powerful 610 motor. What I had considered excessive damping with the high revving 350 motor seemed welcome with the torquey hard hitting 610 motor. The 1992 Showa Husqvarna suspension is definitely a lot different than the 1991 White Power Husqvarna suspension, and I have to say that I much prefer the 1991 White Power to the 1992 Showa. What the 1992 Showa does well is stay planted over water bars, large ditches and all types of small jumps. The low speed rebound damping on the 1992 Showa suspension is substantial, and this keeps the bike well in control and low to the ground over bumps and jumps. This large amount of low speed rebound damping also means that the Showa suspension can pack up over even quite widely spaced bumps, and this makes it slow on many types of real off road terrain.
The 1992 Showa suspension is heavy on the always on compression damping, and this makes it harsh and uncomfortable to ride. The combination of this harsh always on compression damping and a hard and narrow seat leads to a sore rear end on longer rides and the 1992 Husqvarna is generally not comfortable to ride anywhere other than a short well groomed trail or track. I added another layer of softer foam over the seat and recovered it with new material to soften the ride. This did help make the bike rideable over longer distances, but the harsh suspension still means that the 1992 Showa likes to stay well away from rough and rocky dirt roads.
The 1992 Showa Husqvarna suspension is also quite light on any other kind of compression damping, making it bottom extremely easily and slowing the bike down considerably in real off road terrain. What this lack of additional compression damping does do though is allow the 1992 Showa suspension to soak up water bars and steep lipped jumps with a great appetite. Jeremy McGrath would have loved the 1992 Husqvarna for staying low over the jumps on a suppercross track.
The 1991 White Power suspension on the other hand is both supple and compliant while also being able to absorb big high load impacts with great ease. For long rides on any type of trail or dirt road the supple and comfortable 1991 White Power Husqvarna suspension is just great, and the wide and soft seat of the 1991 Husqvarna goes along well with this compliant suspension for making a great long distance endurance cruiser. The extremely minimalistic rebound damping on the 1991 White Power Husqvarna suspension also makes the bike wicked fast over the roughest off road terrain imaginable. There is never any packing up, and no matter how big the bumps the 1991 White Power suspension is always ready for more.
The downfall of the 1991 White Power suspension is that it tends to kick up off of water bars and sharp lipped jumps. This kicking up tends to make the 1991 Husqvarna slow on a motorcross track, but the limitations can be overcome to a large degree by sophisticated riding techniques. The biggest thing that can be done to prevent the kicking up is to plow the front end into the lip of the jump. With the front end well compressed cresting the lip the bike stays lower and the throttle can be chopped without the rear end lifting when going airborne. This is not the easiest thing to accomplish jump after jump, but it is a way to get the 1991 to keep up with the 1992. Of course the new technique of scrubbing the jumps seems tailor made for the 1991 White Power Husqvarna suspension as well. I have long laid the 1991 Husqvarnas over on water bars and other medium size bumps in the trail, but I would never have imagined that the same technique could be used on a big double on a motorcross track.