how do I make my 426 suspension softer

[JK]

I use my 426 for trail riding and find myself wishing the suspension was more plush like the ktm 400. I am 170 lbs and use the bike more for pleasure riding than racing. I have installed a 10 oz. flyweel wieght and jetted the carb. a little richer. All I need to do to have a really good trail is soften up the suspension. Any help would be appreaciated.

[Boit]

JK: I don't know if this would be an option for you since it involves a bit of an expense. I used MX-Tech to revalve and install the correct springs for me and my ability. There are several other shops including RG3 who can give you what you want. Working on the suspension internals is my weak point so I can't advise you there. Some of the other forum readers probably can guide in this area.

[4banger]

What is your impression of mx-tech's work.

[Boit]

4banger: Disregarding the cost, I'm very pleased with the MX-Tech suspension work. I've already shaved 6 seconds off my lap time at the local track I ride most. I feel the best improvement through whoops and hard landings.

[endo]

Try racetech Gold valves. I don't have any personal experience with them, but other yz owners haved raved about them. They also have a verry informative web site. ?

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Endo

'96 KTM 300e (for sale)

'00 YZ426

[fanflv]

I use RACETECH valving kits and springs

best money I spend, you can check out there web site at race-tech.com

I a 190lb rider and ride desert in Nevada.

I totaly recommend using race tech.

[G-Man]

Test

[DaveJ]

JK,

This is a sensitive subject for me since I have accidentally gone through every possible modification one can do to these forks.

Here's that I’ve learned.

First and foremost - Yamaha and KYB have spent a significant amount of time designing these forks and they have done a great job. Unlike the past, I doubt you'll see any aftermarket mods making significant strides in performance.

Secondly- and this is your problem, the forks are set up for high-speed circuit racing. It's a race bike.

Lastly, as you may have already discovered, moving out the settings on the compression screws does not remedy the stiffness issue, and only makes the front end feel springy and sloppy. What you need is a plush but firm ride.

And if you weigh more than 160lbs, softer springs won't do any good either.

The problem is the valve stack. This is a collection of very thin internal shims that are stacked against the openings of the valve.

The fork oil flows through the valve and is restricted by the deflection of these shims. How many shims you have and their thickness is what controls the volume and nature of how the oil flows through the valve.

On the 426, the valve stack is a two-stage valve stack. This means that there is a low-speed and high-speed stack, stacked together. When the forks move in at a slow rate, say going up a jump or some large woops, the low speed stack is in effect. When you hit a series of small bumps very fast, the forks move in very quickly, and the high-speed stack comes into effect, (it's a little more complicated than that, but that's good enough).

In an attempt to fix this, I switched over to a RaceTech Gold Valve. With this, they supply a collection of different valve stack configurations, allowing you to vary the stack according to your riding style and conditions. They also recommend that you remove what's called a mid-valve, which I did as well. All of which is not a quick job.

But problem solved. No more harsh ride, no more blisters and arm pump. Then over time my seal-heads failed and I lost all compression and rebound. This was due to an improperly spec'd mid valve modification by RaceTech. So I went out and purchased some new compression tubes from Yamaha (seal-heads not sold separately...$$$$) and left them as is, (mid valve back in). Result - ride restored.

Then it became a matter of fine turning the ride.

Over time as my riding and jumping progressed, I quickly noticed that the forks were no longer able to meet my expectations. So I tried just about every RaceTech valve stack combination there is. Nothing worked.

So I re-installed the factory valve, but removed some of the high-speed valve stack shims, (they call this coming full circle).

The result - suspension nirvana, (at least this week). The ride was so much better than anything I could get with RaceTech I would have to recommend that they not be used.

During the process of this changeover, I examined the two valves (Yamaha and RaceTech) and noticed that the Yamaha valve is far more sophisticated. In other words, KYB spent a lot more time designing this one than Race Tech spent designing theirs. That’s what you get when you spend five grand on a bike.

Although Race Tech is well known and their team has resolved many suspension issues on earlier models, (and customer service was always helpful) I think their solutions for the later model YZs are outdated and under designed. Keep in mind that the Gold Valve is the same valve design they recommend for all forks, which for later model technology seems….umm…obtuse?

So the bottom line is this. I now have a process where I can make valve stack mods in about 30 minutes or less. As I could have done from the very start if I had been as…umm…well knowledged…as I am today.

I can share how to do this, as well as the stacks that I am using at the moment. The valve is removed with the fork up-side-down, so you’ll still need to take them off the bike, but not apart. You won’t need any special fork tools, but you will need an impact gun, (air or electric) a 14mm hex socket, (SnapOn.com has them) and an inch pound torque wrench. And a file and some other general tools of course.

So…that's enough bashing for one day. Hope this helps and perhaps this will lead to resolving your problem.

DaveJ

[Scott_F]

JK queried: how do I make my 426 suspension softer?

DaveJ, I have to disagree with many of your statements. Nobody has tried every possible mod. Two that I have tried that you may not have, are bottoming cones, and Race Tech type II fork valves. These aftermarket mods can and do significantly alter and improve the fork action.

IMO, the stock forks are nearly unridable, with harsh initial travel, yet easy bottoming. And yes, good results can be had revalving with any pistons, but none will have as high of a flow rate as the Race Techs. If I was to ride this bike in tight slow woods, I would be very willing to use lighter springs, RT type I pistons, and I would lighten the midspeed valve, which is on the top side of the rebound piston. For open fast trails I would keep the stock springs, and valve closer to MX settings.

For reference, I am 6' and 165, and I run stock springs. I am an expert level rider, and do 100' jumps. I no longer have a bottoming problem.

BTW, I would be interested in your old cartridge tubes if you still have them.

Scott F

[DaveJ]

Scott,

Thanks for the feedback - and...you're right, I have not tried everything. What I meant to say is that I tried enough variables with the Race Tech valve to say with a high level of confidence that the factory valve offers better performance. Just my opinion.

Regardless of low and high speed valve stack combinations, springs, mid-valve modifications, and oil level and type, nothing provided me with a better foundation to work with than the factory valve, with mid valve installed, and a modified low and high speed compression stack.

Now if I wanted a very soft ride, perhaps less of a mid-valve would be in order. I don't know.

As for flow rate, I would have to disagree that this is not the best way to measure a quality design. I would say it's a matter of how smooth and progressive a valve is. I.e., is it as smooth at a fast rate as it is at a slow rate? This is where I think Race Tech's marketing is bit mis-directed since they feel that the size of the valve (them big holes) is the most important attribute.

Lastly, I think most of the 426 owners that don't like the harshness of the current ride would be very satisfied with a ride that simply had a few more shims removed off the high speed stack. The stuff you're getting into is a bit more fine tune.

Oh well.

In either case, it's a good little debate and I'm glad someone on this board can talk down to the details as you can.

And where abouts do you live? It'd be cool to swap bikes on a ride and get a feel for each other’s tuning techniques. I'm in the San Jose-CA area.

Let me know.

DaveJ

[Scott_F]

I think the best test of pistons would be to leave the shims alone, and swap out the pistons. That would be the only accurate way to see what effect the flow of the pistons has on overall feel. Then it would be interesting to take out the shims, and ride some chop to feel how they flow.

If stock type pistons flow more than required for the worst curb hits, then Gold Valves would be unnecessary.

Valving and suspension feel are a very personal and subjective thing. The most important thing is to experiment, and get an understanding of how changes affect feel. I live in the LA area, and ride all the local tracks. My bike is setup for SX style, with great bottoming resistance, and a firm yet somewhat plush initial travel. It sucks on choppy bombed out tracks with no airtime.

I will be rebuilding my forks soon, since the seals are weeping, and I want to find a bit more plushness.

Scott F