It started out with finding a used White Power shock that was advertised as being for a 1991 Husqvarna. That's nothing so unusual, but there was a photograph on the listing that clearly showed "TC/TX" stamped in the shock body. Not a 1991 Husqvarna WMX 610 White Power shock, but not an Enduro shock either. I was intrigued.
Drum Brakes and White Power Shocks
1994 KTM 125 MXC 40mm USD White Power Damper Cartridges
The 1991 KTM 250 MX White Power Shock
1991 KTM White Power Suspension for the 1999 Husqvarna WMX 410
A Starting 410
I ordered the "1991" White Power shock as the price was very reasonable at just over $100 delivered. When the package arrived I was shocked to find that it didn't fit on the 1991 Husqvarna bikes. The overall length was the same and the style of mounts were the same, but the reservoir faced back instead of forward so it wouldn't clear the 1991 sub frame.
What I figured out rather quickly was that it was a shock for a 1988 or 1989 Husqvarna. It even had "88" stamped on it, and sure enough it went right on my 1987 Husqvarna 430 WR in place of the 1987 Ohlins shock. An exact fit. So there were White Power shocks on some of the later Italian made drum brake equipped Husqvarnas. Very interesting. This shock was stamped "TC/TX510" and "88", so it came off of a 1988 or 1989 Husqvarna 510 XC or a 1988 or 1989 Husqvarna 510 MX. It could have been a 1990 Husqvarna 510 also, as some of the left over 1988 through 1989 drum rear brake equipped Husqvarna bikes were apparently sold new as 1990 models.
What was even more interesting was that the "TC/TX510" White Power shock did indeed have the more competent racing valving. As soon as I headed off on the 1987 Husqvarna 430 I was blown away by how much smoother and faster the bike was with the White Power shock in instead of the crappy harsh Ohlins shock. Just hugely drastically smoother and more comfortable at all speeds above about 30mph, and even down at very low 20 and 25mph speeds the ride was just about as good as the Ohlins shock. Not only smoother and more comfortable, but loads faster also. The rear end stayed in contact with the ground much better for stronger drive traction and the bike was much more stable and in control at elevated speeds over all types of terrain. A drastic improvement.
Not all was great though. The used "TC/TX510" White Power shock was leaking out the shaft seal, and there didn't seem to be any response from the compression clicker. Even worse the 1987 conventional Husqvarna forks weren't anywhere near good enough. Under heavy braking form high speeds the front end got extremely harsh, and the front end just felt very harsh and uncomfortable under nearly all conditions. Added to that was the imprecise handling of the wet noodle conventional forks, and the front end just wasn't anywhere near up to the task of matching the White Power suspended rear end. The conventional Husqvarna forks had to go. But what to replace them with?
I still had my extra set of 1991 Enduro forks off of the 1991 Husqvarna WXE 350, but I really didn't want to use the crappy harsh and slow Enduro valving on the powerful 430 two stroke. What I really needed was another set of 1991 Husqvarna WMX 610 White Power damper cartridges, but those are very hard to come by.
What I came up with was that there must be some other good damper cartridges available for the 40mm USD White Power forks. The same 4054 "Multi-Adjuster" White Power forks were available on a variety of Husqvarna, KTM and ATK dirt bikes from the 1980's and 1990's, so it seemed like parts should be available. What I eventually figured out was that although the exact same 4054 Multi-Adjuster model forks that came on the Husqvarnas were only available on a few years and models of KTM bikes there were actually a large number of European bikes that came with similar 40mm USD White Power forks that used the same 40mm fork seals and had similar looking compression clickers. Even though the upper tubes were different and the cast aluminum pieces on the bottoms of the lower tubes were very different I figured that the damper cartridges might have the same mounting points.
I ordered a set of 1994 KTM 125 MXC White Power forks. When they showed up I pulled the damper cartridges out, and sure enough they were very similar to the Husqvarna damper cartridges. The all aluminum rebound clickers on the 1994 KTM forks were different, and they required the use of the 1994 KTM caps. And those 1994 KTM caps and rebound clickers had to be used with the 1994 KTM damper cartridges as the drive for the rebound adjuster was a different shape than on the Husqvarna White Power forks. Those 1994 KTM fork caps did however thread right into the 1991 Husqvarna fork tubes. The cartridges were indeed interchangeable, but the 1994 KTM cartridges required the use of the 1994 KTM caps and rebound clickers as a matched set.
The 1994 KTM 125 MXC forks also came with the slightly lower spring rate 513g fork springs with 0.181" diameter coils and 0.31" air gap between the coils, which seemed like a good match for the slightly lighter 1987 Husqvarna two stroke.
It was looking fairly good for the 1994 KTM 125 MXC damper cartridges, and when I installed them in the 1991 Husqvarna WXE 350 fork tubes the overall length came out in-between the WXE forks and the 5/8" longer 1991 Husqvarna WMX 610 forks. Since my past experiences had been that the 5/8" shorter 1991 White Power forks always had the inferior valving this longer overall length was encouraging.
Next I had to try to guess what weight of fork oil to use. The 1994 KTM 125 MXC forks came with rather thick looking fork oil, and there were some other clues also. The 1994 KTM 125 MXC cartridges actually looked more like the 1989 Husqvarna 510 White Power cartridges (See A 1987 Husqvarna 510 XC with Newer Forks).)
The 1994 KTM 125 MXC damper cartridges had the same loose lower spring perch as the 1989 Husqvarna 510 "TC/TX" damper cartridges as opposed to the welded on lower spring perch of the 1991 Husqvarna White Power forks. The combination of the forks having come with thick looking oil in them and that similarity to the 1989 Husqvarna White Power forks led me to believe that the 1994 KTM 125 MXC forks were going to need thicker fork oil.
I used the lower spring rate 1994 KTM 125 MXC springs instead of the stiffer 1991 Husqvarna WXE 350 springs and I filled the forks with ATF. The 1994 KTM 125 MXC damper cartridges not only have different looking rebound clickers, but the clicks are different also. Instead of seven positions like on all the Husqvarna 40mm USD White Power forks the 1994 KTM 125 MXC damper cartridges have 24 positions, and the knobs turn around nearly three full turns versus just over one turn on the Husqvarna 40mm USD White Power forks.
I started out with the rebound clickers in 10 clicks, but wow that was way too much rebound damping! The front end went down and didn't come back up! Next I went all the way out on the rebound clickers, and this did drastically decrease the rebound damping. There actually still was some significant rebound damping with the clickers all the way out on the approximately 15W oil, but it was minimalistic. It was just about enough rebound damping for the bike to work, but I felt like it needed more rebound damping to stay well in control at higher speeds. I then went in three clicks on the rebound clickers, and that seemed just right; very substantial rebound damping, but not excessive feeling. So it's an absolutely huge response from the rebound clickers on the 1994 KTM 125 MXC damper cartridges, that's interesting. And it felt like very good competent rebound damping that kept the bike well in control at all higher speeds without packing up or feeling excessive.
The compression damping on the 1994 KTM 125 MXC damper cartridges was a different story; very little response from the compression clickers and not much hold up on jump landings. It felt pretty much exactly like the compression damping on the 1989 Husqvarna 510 XC 40mm USD White Power forks on my 1987 Husqvarna 510 XC. Going all the way in on the compression clickers with 15W oil on the 1994 KTM 125 MXC damper cartridges certainly did result in some substantial compression damping, and it was pretty good compression damping also. Not quite as good as the 1991 Husqvarna WMX 610 40mm USD White Power forks, but darn good none the less. Going all the way out on the compression clickers on the 1994 KTM 125 MXC damper cartridges resulted in a minimum sort of compression damping that also worked quite well. Unsurprisingly I picked the same #3 compression damping setting that I had picked on the 1989 Husqvarna 510 XC White Power forks. That resulted in some usable hold up for general purpose riding while retaining a fairly smooth and comfortable ride under all conditions. The front end of the 1987 Husqvarna 430 two stroke felt good with the 1994 KTM 125 MXC damper cartridges. Rather smooth and comfortable under all conditions, and also substantially damped and well in control at all speeds over all types of terrain.
Probably the most interesting thing about the 1994 KTM 125 MXC damper cartridges on the 1987 Husqvarna 430 two-stroke was that the damping felt well matched to the flat "TC/TX" White Power shock. There was no response from the compression clicker on the flat shock, but there wasn't much response from the compression clickers on the KTM damper cartridges either. This might sound very bad, but on the somewhat lighter weight 1987 Husqvarna two-stroke it actually seemed to work just fine. With a "56" spring on the shock the rear end didn't seem to bottom all that easily, and the bike was very ridable. Not exactly a supper aggressive motocross setup, but very usable none the less. It would be nice to be able to dial in more hold up at both ends for aggressive riding on a motocross track or in the sand dunes, but the 1987 Husqvarna 430 two-stroke certainly was usable just like it was with a flat White Power shock and the somewhat lackluster 1994 KTM 125 MXC damper cartridges in the forks.
The improvement over the stock 1987 Husqvarna conventional forks and the stock 1987 Ohlins shock was quite drastic. Even with the lighter weight of the two stroke the White Power suspension is a whole lot smoother and more comfortable at pretty much all speeds. Yes, the Ohlins shocks are very smooth and comfortable at very slow speeds on extremely rough tight trails, but open class power doesn't stay going slow very well. The White Power suspension is just a whole lot faster, and that is a good match for a powerful open class engine. Even on a lighter two-stroke.
As with the White Power shock upgrade for the 1987 Husqvarna 430 two-stroke the White Power shock upgrade for the 1999 Husqvarna TE410 came in a round about sort of way. Again I was actually looking for a shock that would fit on the 1991 Husqvarna bikes, and again I was looking at various KTMs from the 1990's that came with White Power shocks.
What I came up with was a 1991 KTM 250 MX. It has a White Power shock that is similar to the White Power shocks on the 1988 through 1991 Husqvarnas, but there are some differences. The shock body is a different shape on the 1991 KTM 250 MX White Power shock; the reservoir mounts up higher, where the reservoir mounts down rather low on the 1988 through 1991 Husqvarna White Power shocks. The reservoir on the 1991 KTM 250 MX White Power shock also mounts nearly straight out the side, although it is the other side of the KTM! Looking at photographs of used KTM shocks listed on eBay I was convinced that the different reservoir location would in fact clear the 1991 Husqvarna sub frame.
When I got the 1991 KTM 250 MX shock I found that it's actually very far from fitting on the 1991 Husqvarna chassis. The 1991 KTM 250 MX shock is much longer at 17-5/8" from eye to eye. The lower mount is also wider on the 1991 KTM 250 MX shock.
The 1991 KTM 250 MX White Power shock actually didn't fit on the 1991 Husqvarna chassis at all with the stock reservoir. The 1991 KTM 250 MX White Power shock has a longer reservoir like the long reservoirs on the White Power shocks on the 1990 and 1991 Cagiva/Husqvarna two strokes. Even though the reservoir mounts much higher on the 1991 KTM 250 MX shock it's not angled forward like on the 1991 Husqvarna White Power shocks. The 1991 KTM 250 MX White Power reservoir actually does end up angled very slightly forward when mounted so that the reservoir sticks out the left hand side of the bike, but it's only very slightly forward. On the 1991 Husqvarnas the reservoir is angled rather steeply forward to clear the 1991 sub-frame.
Determined to see how the 1991 KTM 250 MX shock would work I swapped out the reservoirs to put one of my Schrader valve equipped Enduro Husqvarna reservoirs on. The first challenge I ran into is that the shape of the 1991 KTM 250 MX shock body creates a big void directly above the reservoir. This makes it much more difficult to get all the bubbles out of the shock. I did eventually figure out how to get all the bubbles out, but it was a bit of a challenge. What I came up with was to fill the shock with oil and then put just 15psi in the bottom of the reservoir. With just a very low 15psi bellow the reservoir piston I tipped the shock over at about a 45 degree angle and unscrewed the reservoir to release the bubbles from above the piston. This is similar to how I had previously gotten the bubbles out of the Husqvarna White Power shocks, it just took tipping the shock over more and repeating the procedure several times to get all the bubbles out of the 1991 KTM 250 MX White Power shock. Taking the spring off and working the shaft in and out several times with the shock upright also helps to work the bubbles up out of the shock and into the reservoir area where they can be bled off.
With all the bubbles out of the 1991 KTM 250 MX shock I pumped it up to 90psi and the shaft seal held with no leaks. So far so good.
Mounting the 1991 KTM 250 MX shock on the 1991 Husqvarna chassis was not easy. A stack of washers was required to make up the difference in width of the forked lower mount, and the considerable extra length really didn't fit. I did get the shock stuck on for a test ride though. Wow, also the better White Power damping. That's great!
Unfortunately there was hardly any response from the compression clicker on the 1991 KTM 250 MX shock. There was some response from the compression clicker, but it was just hardly anything at all. Even going up to the #7 compression clicker setting it seemed like there wasn't enough hold up landing from even small jumps. The ride was very similar to a 1991 Husqvarna WMX 610 White Power shock, but the valving seemed subtly different. Good, but slightly different. A bit more bouncy feeling, like the rear of the bike was bouncing up more over medium sized bumps.
In trying to get the compression damping working I tried many different things. The first time I actually didn't quite get all the bubbles out of the 1991 KTM 250 MX shock, so I even more thoroughly worked the bubbles out by un screwing the reservoir with just 15psi under the piston. The compression clicker still didn't do much of anything.
Next I took the plastic knob off of the compression adjuster. With the knob removed I turned the shaft all the way in to where the compression adjuster shaft bottoms out, but this didn't deliver any more hold up. I rode the bike around with the knob off and turned the shaft from one extreme end where the adjuster is seated down at the bottom out to the other extreme end where oil starts to seep past the adjuster shaft seal. That's about two full turns, but still there was hardly any response at all from the compression adjuster. It just seemed the same everywhere.
Next I took the compression adjuster itself out of the 1991 KTM 250 MX shock body. I didn't take the adjuster apart, I just took it out of the body. I then took the compression adjuster out of a Husqvarna Enduro White Power shock that had huge response from the compression clicker. That's actually another side story in itself.
I liked the White Power upgrade on the 1987 Husqvarna 430 two stroke so much that I was looking for another one of those 1988 or 1989 White Power shocks to go on my 1987 Husqvarna 510 XC. All that seemed to be available were the Enduro "TE" stamped White Power shocks, so I tried one of them. I had the 1989 Husqvarna 510 swing arm that came with the 1987 Husqvarna 510 XC and I had an extra 1991 linkage, so I thought I could just slap a White Power shock right on. Wrong! It turns out that the shock mount is actually lower on the 1985/1986 Husqvarna frames. Since my 1987 Husqvarna 510 XC is an early model that uses the 1986 style swing arm and linkage it also has the lower shock mount. Again undeterred I stuffed the 1988 Husqvarna 510 "TE" White Power shock on and when for a test ride. By backing off on the pre-load a large amount using a shorter spring I got the rear end to sit at the correct height, and the bike sort of worked. The "TE" stamped 1988 White Power shock however turned out to have the same crappy Enduro valving as the three 1991 Husqvarna WXE 350 White Power shocks I have. The same ineffective rebound damping that won't keep the bike well in control and the same harsh uncomfortable ride at all elevated bike speeds. The compression clicker on the 1988 "TE" White Power shock did work. Going in two clicks resulted in a huge increase in compression damping, it's just that it didn't do any good on the already far too harsh riding "TE" Enduro valving. The compression clickers always seem to work on those "TE" Enduro White Power shocks, it's just that the valving is so harsh and uncomfortable that you wish the compression clicker didn't work.
So that's the shock that I took the known functioning compression adjuster out of. It looked exactly the same as the 1991 KTM 250 MX compression adjuster. With the 1988 "TE" compression adjuster installed in the 1991 KTM 250 MX shock performance was exactly the same. Not the slightest bit of difference. Exactly the same good compression and good rebound damping from the 1991 KTM 250 MX shock, and exactly the same very small response from the compression clicker.
I still didn't have the 1991 KTM 250 MX shock working acceptably, but I had learned something very interesting. The lack of response from the KTM compression clicker is due to the internal parts of the shock. The compression adjusters themselves appear to all be exactly the same, they just work differently with different amounts of oil flowing through them. The reason that the 1991 KTM 250 MX shock has only a small amount of response from the compression clicker is that the 1991 KTM 250 MX shock pumps less oil out to the reservoir. Lower oil flow rate, less response from the compression clicker. That's interesting.
In then end though it was just the fact that the 1991 KTM 250 MX shock doesn't fit on the 1991 Husqvarna chassis that was most significant. Upward travel of the rear wheel was still exactly the same, as the compressed length of the 1991 KTM 250 MX White Power shock is exactly the same, as the compressed length of the Husqvarna White Power shock. That makes the 1991 KTM 250 MX shock seem to sort of work on the 1991 Husqvarna chassis. It doesn't work though. The rear wheel hanging way down so that the linkage stops the shock instead of the shock stopping the linkage just doesn't work at all on a Husqvarna. Increased rear wheel travel might be considered desirable, but the 1991 Husqvarnas already have a huge thirteen inches of rear wheel travel.
The 17-5/8" length of the 1991 KTM 250 MX White Power shock didn't work at all on the 1991 Husqvarna chassis, but then I realized what other bike has a 17-5/8" eye to eye shock length: The 1992 through 2001 Husqvarnas. It's a 17-5/8" long Showa shock on the 1992 through 1998 Husqvarnas and it's a 17-5/8" long Sachs shock on the 1999 through 2001 Husqvarnas.
At first I didn't jump to put the 1991 KTM 250 MX on either of my later Husqvarna bikes. The reason I was reluctant to make the upgrade was that I still didn't have good forks for either my 1992 Husqvarna or my 1999 Husqvarna TE 410. What use is a good shock with crappy forks?
The solution was another set of KTM damper cartridges. I ordered a set of 1991 KTM 250 MX 40mm USD White Power forks, figuring that they would be a good match for the 1991 KTM 250 MX White Power shock.
When the 1991 KTM 250 MX forks showed up I was very disappointed to see that they looked short like the crappy Enduro White Power forks. I decided to give the damper cartridges a try anyway though. The KTM 250 MX White Power forks use red plastic rebound clickers and the same style of caps as the Husqvarna White Power forks. The 1991 KTM 250 MX caps are however stamped "K" to indicate KTM, so I was still hoping for some good valving.
When I got the damper cartridges out it was interesting to find that they are in fact longer like the 1994 KTM 125 MX damper cartridges: About 5/16" longer in extended length than the crappy 1991 Husqvarna WXE 350 and the equally crappy 1991 Cagiva/Husqvarna WMX 250 damper cartridges. It was just the different KTM fork tubes that made the forks look short. The 1991 KTM 250 MX damper cartridges actually are the longer travel type.
It was also interesting to find 1991 Husqvarna WMX 610 springs in the 1991 KTM 250 MX forks: The exact same 0.188" coil diameter and 0.31" air gap between the coils. The 1991 KTM 250 two-stroke must be one heavy beast to use the same springs as the 1991 Husqvarna WMX 610!
For my 1999 Husqvarna WMX 410 White Power upgrade project the 1991 Husqvarna WMX 610 springs were welcome: The 1999 Husqvarna TE 410 is every bit as heavy as a 1991 Husqvarna WMX 610. A bit of weight is saved with the aluminum sub frame and lighter plastic, but all of that weight savings is offset by the heavier clutch cover, extra gear in the transmission, kickstand and lights. The 410 cylinder and 410 cylinder head are even slightly heavier than the 610 parts because there is more aluminum filling in the missing displacement. All of the 1991 through 2001 Husqvarna four strokes weigh about the same, with the variations from year to year and model to model being only a very few pounds. A 1991 Enduro bike is the heaviest, and a 1992 Motocross bike is the lightest but the differences are very slight.
I actually ended up doing the entire suspension swap all in one day on the 1991 Husqvarna 410. I had been thinking about using the 1991 KTM 250 MX damper cartridges in my period correct 1991 Husqvarna WMX 610 to replace the poorly functioning suspension shop modified 1991 WMX 610 White Power cartridges. When the 1991 KTM 250 MX forks showed up and looked short though I didn't want them anywhere near a 1991 Husqvarna WMX 610. Instead I decided to go ahead and throw the 1991 KTM 250 MX White Power shock on the 1991 Husqvarna TE 410. That turned out to be harder than I thought it was going to be.
The 1991 KTM 250 MX White Power shock might have the correct 17-5/8" eye to eye length to go on the 1999 Husqvarna chassis, but the mounts were far from fitting. On the lower mount it was just a stack of washers that was required to make up the extra width, but even that wasn't simple.
The first problem I had was that the Sachs shock wouldn't come off. Just like with the 1992 chassis the shock wouldn't come out the top without taking the exhaust off, but on the 1999 chassis the shock wouldn't go down into the swing arm to allow it to come out the back of the bike either. I thought I was actually going to have to remove the exhaust system like the 1992 Husqvarna Owner's Service and Tuning manual recommends. But then I realized that I could just take the air box off. With the air box removed the shock came right out the top like on a 1991 Husqvarna.
The next major challenge was that the top mount is 0.1" narrower on the 1992 through 2001 Husqvarnas. The top mount on the 1991 KTM 250 MX White Power shock is the same width as the top mounts on the 1988 through 1991 Husqvarna White Power shocks, so that ended up being 0.1" too wide for the 1999 Husqvarna chassis. The diameter of the top bearings looked about the same on the White Power shocks as on the Sachs shocks, so I thought I could just swap the entire top mount bearing.
The top mount bearing came right out of the 1991 KTM 250 MX White Power shock, but I couldn't get the top mount bearing out of the Sachs shock. When I put lots of pressure on the bearing in the 20 ton shop press it eventually popped out. Literally popped! There was a hidden snap ring holding the Sachs mount bearing in place, and the bearing didn't come out until the snap ring "snapped" out of the shock body taking a ring of aluminum with it.
Then I realized that the outside diameters of the bearings aren't the same after all. In the end I had to cut down the 1991 KTM 250 MX White Power top mount bearing. This was easy enough, but it had taken several hours of frustrating thrashing in the rising heat to finally get to that point.
With the top mount bearing modified the 1991 KTM 250 MX White Power shock slipped right into the 1999 Husqvarna chassis. Once bolted up the cut-down upper mount is invisible, and the stacks of washers on the lower mount are fully hidden inside the big 1999 drag link. The 1991 KTM 250 MX White Power shock looks like it was made for the 1999 Husqvarna TE 410, although the reality is exactly the opposite. The 1992 through 2001 Husqvarnas were made for the 1991 KTM 250 MX White Power shock!
Adding to the factory look is the big yellow and blue "Husqvarna Supper Adjuster" sticker on the Husqvarna White Power reservoir I screwed onto the 1991 KTM 250 MX White Power shock, although the sticker does come out facing to the right hand side of the bike instead of to the left side of the bike when the Husqvarna White Power reservoir is installed on the 1991 KTM 250 MX White Power shock.
The shock upgrade was the hard part. Stuffing the 1991 KTM 250 MX White Power damper cartridges into the 1991 Cagiva/Husqvarna WMX 250 White Power shocks that were already installed on the bike was easy.
The oil that came out of the 1991 KTM 250 MX forks was very thin, so I decided to use 5W fork oil. This turned out to be the correct guess. As soon as I rode off on the 1991 KTM 250 MX suspended 1999 Husqvarna 410 I was very impressed. Wow, so much smoother and more comfortable than the 1999 Husqvarna 410 had ever been before. Wow, just a huge difference. And the suspension seemed to work darn good when pushed hard.
There was one small problem that showed up right away though. The 1991 KTM 250 MX damper cartridges felt a bit harsh over sharp edged bumps at higher speeds. It was a slight problem, but it was there. It was only that one little problem though. Under nearly all conditions the 1991 KTM 250 MX suspension felt really just perfect on the 1999 Husqvarna 410. It felt very much like a 1991 Husqvarna WMX 610, and overall performance was stellar.
The 1991 KTM 250 MX White Power shock felt better on the 1999 Husqvarna than it had on the 1991 Husqvarna. There is a difference in linkage rates, and unsurprisingly the 1991 KTM 250 MX shock worked much better with a linkage that was actually designed for it's longer shaft travel. The rear end of the White Power upgraded 1999 Husqvarna 410 felt really very much like the rear end on a 1991 Husqvarna WMX 610: Smooth and comfortable and also substantially damped and well in control. Interestingly the lack of response from the compression clicker didn't seem like as much of a problem either. There still wasn't all that much hold up, but it felt like enough and the bike seemed to work very well.
The front end was very good also, but there were some strange things going on. The harshness hitting sharp bumps at high speeds was one problem, and it was only a rather slight problem. It was very surprising though. How could forks for a 250 two stroke feel excessively stiff and harsh on a 410 four stroke? It just didn't seem right. When I tried turning the adjusters on the 1991 KTM 250 MX forks I was equally confused. There didn't seem to be any response at all from any of the clickers, or at least hardly any response.
I had started out at the #2 compression clicker setting, and when I tried going up to the #4 compression clicker setting hardly anything happened. There was perhaps a very slight bit more hold up and the forks didn't seem to get harsher or more uncomfortable, but the change was miniscule. Then I went all the way out on the compression clickers, and again there was hardly any change at all.
On the rebound side even less happened. I had started out at the #3 rebound setting, and going up to the #5 rebound setting didn't seem to do anything. Then I went all the way out to the #1 rebound setting, and again there was no change. The rebound clickers didn't seem to do anything at all, and the compression clickers hardly seemed to do anything.
Overall though the 1991 KTM 250 MX suspension is excellent. It might not have much of any adjustability, but it is darn good even without being adjustable. Certainly a vast upgrade over the stock 1999 Husqvarna TE 410 suspension, and also way better than the crappy 1991 Husqvarna WXE 350 White Power suspension. The 1991 KTM 250 MX White Power suspension valving is virtually identical to the 1991 Husqvarna WMX 610 White Power valving, and that is a very good thing.
For the owner's of 1991 Husqvarna four strokes there is an interesting lesson in all of this. Watch out that your clickers don't stop working, or your Husqvarna might turn into a pumpkin! If your 1991 Husqvarna is a WMX race bike then turning into a pumpkin is a bad thing because a lack of response from the compression clickers means that all that weight and all that power is going to be a lot harder to apply to a wide range of conditions. If your 1991 Husqvarna is a WXE Enduro model though then you want it to turn into a pumpkin! The 1991 KTM MX valving is quite a lot better than the Husqvarna Enduro valving.
Just as I had predicted early in 2017 it was the crappy suspension valving that was the main obstacle to easy starting on the 1999 Husqvarna TE 410. Once I got the fairly good working 1991 KTM 250 MX White Power suspension installed on the now truly upgraded 1999 Husqvarna WMX 410 I turned to the engine problems. First of all it was an oil leak. There had been lube oil dribbling down the front of the 410 motor since I first got it. Back then in early 2017 there was a huge accumulation of old dried on lube oil all over the front of the engine as if there had been a persistent oil leak. I cleaned that gunk off when I installed the new Woessner piston, but then the oil leak continued after I assembled the engine. I thought it might be the exhaust valve adjuster cover, although it did sort of look the lube oil was actually coming out from under the rocker cover. There was also some wet oily residue around the breather, so I really wasn't entirely sure where the leaking oil was coming from. Again though I just didn't have any interest in working on the 1999 Husqvarna 410 as long as the suspension wasn't good enough. If I couldn't ride it I didn't care what else was wrong with it. I might have just sold it, but I couldn't bring myself to subject anyone else to that crappy harsh suspension either. Instead the bike just sat there.
With the 1991 KTM 250 MX White Power suspension working fairly well I was all of a sudden motivated to get the rest of the 1999 Husqvarna 410 in top shape. That oil leak was first up. I took the valve adjuster covers off, adjusted the valves and glued the covers back on with lots of RTV silicone both on the gaskets and on the bolts that go through to oil. Nope, not the problem. On the first little test ride the oil was back running down the front of the engine just as severely as ever.
This fairly clearly indicated that the problem was at the rocker cover; a much more difficult repair. I took the tank off for the second time in the same day, and this time I had to go deeper by draining the coolant and pulling the water pump off. When I got the rocker cover off I immediately saw what the problem was. There was a big thick pile of lumpy RTV silicone at the front of the cover, and the rest of the sealing surface was clean looking with just the thinnest layer of squished down RTV silicone. The problem was a big two inch wide by approximately 1/32" deep chunk of the sealing surface simply missing. Where had it gone? Who knows. Maybe it was like that from the factory back in 1999. In any case that was the source of the lube oil leak. It looked like a fairly big chunk missing, but I figured it would just fill up with RTV silicone. The only reason it hadn't sealed the first time was that I had applied only a very thin smearing of RTV silicone to the sealing surfaces on the rocker cover and the cylinder head. It just wasn't quite enough RTV silicone to fill the big void. On all the other Husqvarna rocker covers a very thin smearing like that is always plenty, and I have never had the slightest bit of trouble with oil leaks from any of the other rocker covers I have installed.
Sure enough just cleaning the cover and cylinder head up thoroughly and adding a big pile of RTV silicone to that missing void did the trick. With the bike back together the oil leak was totally gone.
Next up was the starting difficulty. The gasoline I had was more powerful and was running great in the 410, but it wouldn't kick start once hot. Sometimes it would fire on the first kick and run for a half second before dying, but then nothing on subsequent kicks. It just wouldn't restart with the kick starter. I tried the same gasoline in the 1987 Husqvarna 510 XC, and the energy density seemed a bit low as there was quite a bit of popping out the exhaust on the very lean jetted 510. There had been hardly any popping out the exhaust on the 410, and both 91.5mm bore engines ran quite strong. On the 510 there was some popping out the exhaust, but it was able to restart easily on the first kick, was idling smooth and stable and there seemed to be good throttle response at all smaller throttle openings.
Riding the 410 and the 510 back to back on the same gasoline was interesting. The peak power output seemed so very similar from both engines. Perhaps the 510 made a bit more power, but then again it was hard to say because the top end power from the 410 was really very substantial also. The really big difference was just that the 510 made big power down lower, where the 410 needed to be screaming on the top end to make the big power.
Torque from the 410 was very substantial though, and it was pulling nicely down to around 3,000RPM without any difficulty. It was getting very gnarly under a full load down supper low bellow about 3,500RPM, but the reasonably strong torque was continuing down so low that there was no reason to say that it wasn't pulling well at low engine speeds. It really is keeping the spark timing down at less than 25 degrees BTDC that prevents excess harshness in the difficult 3,000 to 5,000RPM range of engine speeds, and the 23 degree BTDC spark timing on the 1999 Husqvarna 410 motor works really very well.
At small throttle openings the 410 was able to cruise along extremely smoothly and extremely quietly at all lower engine speeds around 2,500 to 4,000RPM. The dual parallel muffler 1999 Husqvarna 410 was also running along without all that much noise. Sometimes the 1999 Husqvarna 410 really makes some obnoxious huge amounts of exhaust noise through those big dual parallel mufflers. On this particular gasoline though the 410 was making nice strong torque and wasn't all that loud. What the 410 also was doing though was turning off somewhat abruptly at the top of the power band; an all too common occurrence for the small valve 410 motor. The gasoline seemed like a mixture of about half slow flame front travel speed regular and about half race gas, and that was just what it had seemed like in the 12.2:1 hot rod 610 motor the day I brought it back from the gas station.
Quite powerful with a rather high overall temperature of combustion potential so there was strong torque and no surging in the 3.01" stroke length 610 motor, but also large amounts of crispness down at 2,500 to 4,000RPM and some reluctance to get going and make power everywhere from 5,500 to 7,500RPM with the big 98mm bore. There was however quite strong power to 8,500RPM without cutting out, the 12.2:1 hot rod 610 motor just needed to be well warmed up on some big pulls to reliably lay down the power at the higher engine speeds. The flame front travel speed seemed sort of in the middle. Not extremely slow flame front travel speed regular, but also not extremely fast flame front travel speed premium or race gas. Is it a mid grade gasoline? Perhaps. Or perhaps it's just half regular and half race gas with a little bit of ethanol mixed in to keep the overall energy density on the low side. Not an extremely low energy density though, as the hot rod 610 motor was hardly popping out the exhaust at all on deceleration and starting performance was very good with reliable easy starting mostly on the first or second kick.
On this more powerful gasoline which wasn't having any trouble supporting the longer 3.01" stroke length the similarities between the 510 and the 410 were more significant than the differences. They are both 91.5mm bore engines, and they both run approximately 23 degree BTDC spark timing. The 410 has a slightly higher compression ratio than the 510, but they both ran very similarly on the same gasoline at the same elevation. The larger displacement of the 510 heats the cylinder head and piston up a bit more easily, so it can deal with the slightly lower compression ratio without much difficulty. The 410 was a bit more instant through the lower midrange right from the first 1/4 mile of riding, where the 510 needed to get warmed up before it seemed perfectly instant. The torque from the 510 was however very reliable, and there didn't seem to be any troubling hesitation once the engine was warmed up.
The other thing that was interesting about riding the 1987 Husqvarna 510 and the 1999 Husqvarna 410 back to back was comparing the suspension. The 1989 Husqvarna 510 XC White Power forks on the 1987 Husqvarna 510 XC certainly are more plush riding and more comfortable than the 1991 KTM 250 MX White Power damper cartridges. At the rear end though it's all advantage White Power. The 1987 Ohlins shock just isn't as good. The Ohlins shock seems very smooth and comfortable at very low speeds, but going faster and pushing the bike harder it all fell apart. That Ohlins harshness that tends to creep in at higher speeds is very annoying. It causes the back end of the 510 to bounce up, both making the ride uncomfortable and also tending to throw the bike out of control at higher speeds.
With the suspension not seeming good enough on the 1987 Husqvarna 510 XC there was all the more reason to want my other 91.5mm bore Husqvarna to start reliably. The first thing I tried was going down to a 0.016" spark plug gap. That seemed to do the trick, as the weak spark "Ducati ignition" 410 motor then fired right up on the first kick three times in a row. But then it again wouldn't kick start. Well, there were other things going on. I had drained the gasoline out of the 410 to put in the 510, so the tank was empty. It was on that empty tank that the 410 had started three times in a row.
With gasoline back in the tank it again wasn't kick starting. I figured that one out though, and I then tried turning the petcock off. If I turned the petcock off and rode for about 100 feet before stopping then the 410 would fire right up on the first kick. If I left the petcock on though it would fire and then stall after a half second and then wouldn't fire at all on subsequent kicks.
Next I lowered the float level by more than 1/8". A huge change in float level for the DellOrto carburetor. That did the trick. The weak spark "Ducati Ignition" 410 motor then fired right up every time on the first kick. It fired up easily on the very first kick about ten times in a row, but then a few times it fired low and weak, stalled and wouldn't fire on subsequent kicks. There was that ten times in a row though, and mostly it was firing up every time very easily on the first kick. Maybe it wasn't the plug gap after all.
So I went back to a 0.023" spark plug gap, and the engine then wouldn't kick start. A few times it did fire back up with the kick starter, but most of the time it just wouldn't fire at all or would fire on the first kick, stall and not restart. It wouldn't start with the wider spark plug gap.
Then I went down to a 0.013" spark plug gap, and again the engine fired up very easily on the first kick every time. With just a 0.013" plug gap though the engine didn't run as well. There was some bobbling and instability at small throttle openings down at very low engine speeds around 1,200 and 1,800RPM that hadn't been present with a 0.016" plug gap. The engine was starting very easily though, and that was impressive. It was also low idling without stalling, and was able to restart even after extended periods of low idling even though the low idle wasn't all that stable.
But then the 410 motor again failed to restart a few times. I just couldn't seem to figure it out. When I went out and rode around shutting the motor off over and over again it was restarting very easily on the first kick every time. Even when I waited quite a while before restarting it just fired right up every time very easily on the first kick. But then confusingly it failed to start sometimes.
Eventually what I figured out was that it was when I laid the bike over on the side stand that it failed to start. Even if I only set the bike on the side stand for a short few seconds and then climbed back on it wouldn't kick start and had to be roll started. The carburetor was filling up to a higher level when laid over on the stand, and that was preventing kick starting. When I tried turning the petcock off before laying the bike over on the side stand it then fired right back up very easily on the first kick.
So the 410 started easily at a 0.013" spark plug gap, and it had also been starting easily at a 0.016" spark plug gap. Next I tried a 0.019" spark plug gap, and that also worked. Again the bobbling and instability was totally gone, and the engine was firing up easily on the first kick every time. As long as I didn't tip the bike over with the petcock turned on!
Then the next problem at a 0.019" spark plug gap was that the 410 motor wouldn't fire back up with the kick starter after sitting for more than a few minutes. After sitting for very short periods of time less than about one minute it fired right back up, but then after sitting for more than just a few minutes it fired on the first kick but ran for only a half second, stalled and wouldn't fire at all on subsequent kicks. After sitting for an hour though the 410 started very easily on the first kick without using the choke. It was only that in between period of time where it wouldn't start. What was going on? Fully cooled off after sitting overnight it also fired up from cold very easily on the first kick without using the choke, although cold is relative on a 100 degree July day.
Pretty quickly I thought up a possible explanation, but I wasn't really sure just how true it might be. My idea was that gasoline was continuing to evaporate up into the intake as the bike sat after being shut off hot. The hot starting difficulties with the Husqvarna 410 motor usually seem to be related to the weak spark "Ducati Ignition" needing an extremely lean mixture to kick start. Turning the idle mixture screw in all the way had gotten the 410 kick starting when hot sometimes, and then both lowering the float level and reducing the plug gap had helped a lot more. Then it was just tipping the bike over on the side stand that was raising the float level that little bit extra and preventing hot restarting.
It's like the short duration weak spark "Ducati Ignition" CDI was just favoring an extremely lean mixture, and it wouldn't tolerate even a slightly richer mixture for hot starting. Just lowering the float level was enough to make the difference, even though changing the float level does only very slightly change the mixture. Just lifting the fuel that 1/8" higher up to the idle circuit does lean the mixture out, but only by a very small amount. Lowering the float level that 1/8" didn't appear to change performance at wider throttle openings at all, although the approximately 157 size main jet is certainly rather fat in the 36mm DellOrto.
The slightly leaner mixture did make a very significant difference in hot starting performance, and changing the plug gap wasn't the panacea that it had been on the long duration weak spark Swedish SEM ignition system. For more on reducing spark plug gaps on the Swedish SEM Husqvarna CDI ignition systems see Resurrecting the 1991 Husqvarna WMX 610.
Reducing the plug gap on the short duration weak spark "Ducati Ignition" on the 1999 Husqvarna 410 did improve starting performance, so it really is a weak spark ignition system that has a hard time bridging the gap through the dense compressed intake charge. It's just that the "Ducati Ignition" also makes a very small spark that seems to be easily put out by too much fuel floating around. The Swedish SEM ignition on the other hand doesn't seem to have much trouble with rich mixtures. At one point recently I took the bowel off of the carburetor on my 11:1 Woessner piston equipped but otherwise bone stock Swedish SEM ignition 1991 Husqvarna WMX 610, and I found the "62" marked original pilot jet out at the 63 size. This hadn't been preventing the SEM ignition motor from starting though. I took that pilot jet out and put in one that I had soldered up and re-drilled to the 61 size. This did seem to improve overall performance from the 11:1 stock SEM ignition 610 motor a bit, but the difference was not large. It had been running fairly well and starting easily with the oversize 63 pilot jet also. And then there was my period correct big cam 1991 Husqvarna WMX 610 that was starting easily and reliably with the stock SEM ignition even when the pilot jet was out at about the 64 or 65 size. Again the motor ran better when I went down to a 61 size pilot jet, but it had been starting on the 64 size pilot jet even on higher energy density gasoline. Very rich low idle mixtures can certainly cause hard starting even with a strong spark, but it has to be pretty darn overly rich.
The short duration weak spark "Ducati Ignition" system seems to be specifically designed to be as intolerant as possible of rich low idle mixtures, which is a strange match for the 1999 Husqvarna 410 36mm DellOrto that seems to have a tendency to run rather rich at low idle. The stock 1999 Husqvarna 410 seems to be designed specifically to not start. That's probably a feature to go along with the horrendously harsh riding suspension. The stock Showa/Sachs suspension is so bad that you really don't want the engine to start. Better just let it sit there and look pretty.