I'm a bit confused and need some help please. I have a 2006 KLX250S. I weigh 165 lbs with no gear. Sometimes I travel with extra gas, sometimes not. I carry at most an extra 20 lbs of gear/fuel for remote rides.

I am in the process of buying parts to re-valve my stock forks. I have re-sprung for my weight, I have changed my fork oil viscosity, I have messed with my air gap (fork oil level). I am still looking for a more supple front end.

I understand valve stacks. I understand the Race Tech solution. I get how things will change if shims are changed. I also understand that the stock fork does not have a rebound circuit, which is problematic.

But...in looking at the schematic for the fork (Babbitt's online has a full breakdown schematic of the fork) I see the only valving sits at the bottom of the fork. It sits there stationary. I see no valving, shim stacks, or other piston that rides up and down through the oil. This confuses me. I am searching for a piston with valving that travels up and down through the oil to give damping. I must be missing something. I'm not understanding how a valve stack, screwed into the bottom of the fork, allows damping. Again...I must be missing something.

Appreciate any help some of you might offer me as I am trying hard to understand this fork.

Mike

 

The shims flex depending on how hard an impact is allowing the flow to match what is needed based on the rider, if they set up the stack, or the manufacturer, in most cases they set up what is desired. I believe the adjustment if there is any will be a spring preload that will adjust, otherwise it is how much pressure it takes to flex the shims to increase flow. A similar process occurs with rebound as well.

There is some rebound circuit in the stock fork, probably a non-variable set up, frequently holes, on top of the damper rod that controls flow a bit when the fork is rebounding.

 

Mike, we communicated on the PM about this a little but didn't talk about rebound. It's been quite a few years since I installed the RT Gold Valve kit for the KLX300 into my '06 KLX250, so I'm a bit fuzzy. There is only external damping control for the compression damping at the bottom of the legs. No external rebound control exists, and this is the biggest disappointment with the old 43mm KLX fork.

Now, there is a rebound circuit in the fork, and this is where my memory isn't as clear. If I recall the rebound circuit is contained inside a tube of the damper assembly. It is unreachable in terms of revalving regardless of not having an external adjuster. The compression damper/shims are at the bottom of the legs and not in a closed damper cartridge. The overall damper design of this fork isn't very sophisticated. Don't take this as fact, but I'm trying to remember if this fork is archaic enough to not even have a shimmed rebound set inside. The rebound could be a simple ported design and only oil viscosity would have any effect. Shimmed or ported, however, it doesn't much matter since you can't reach it and manipulate it from everything I remember.

Here is something I'm going to try and have already obtained the fork oil to do it. The complaint with this fork is that while the compression stack can be tuned quite well for the compression stroke, when you go deep in the stroke, the rebound is not fast enough to allow the fork to be ready for the next hit in the faster, more frequent hits that come in quick succession. Perhaps the compression stack could be manipulated to be even "slower"/"harder" but have the fork oil in a lighter viscosity than the recommended 10wt...maybe 7wt or 5wt...or some mix. Or, see if the current Gold Valve shim stack has enough latitude to run the lighter oil with more turns into the external adjuster to "slow" the compression stroke. Trying the oil change and just tweaking the external adjusters is the easiest to try first, because only the fork oil is invested with little time involved. It's all a bandaid approach, but if it improves it just a little without any real sacrifice in overall performance, it will be worth it.

As you can tell, it hasn't been that terrible for my application as this bike isn't used for competition. The Gold Valves helped tremendously, as the stock setup was terrible. Just to get rid of that occasional spiking on faster, successive hits would be nice.

 

TNC....

Thank you for your response. I was struggling to understand the workings of this fork but you have helped me. I will move forward with Gold Valves to get rid of some of that spike I really hate.

I don't race, don't jump anything big, but do ride pretty aggressively. I want to do what I can to eliminate and supple up the front end as much as I can without spending $1000's. I know KX forks are an option.

Thx again

Mike

 

Glad to see TNC here in time! He has the knowledge most of us wish we did.

 

That $5 is on its way in a plain brown envelope.

 

Same basic design as my '12.
It uses a cartridge tube that contains the rebound valve attached to the rod that connects to the fork cap.
The compression valve is located on the bottom of the fork tube and threads into the bottom of the damper cartridge.
While the compression valve allows access for modifications, the rebound valve is crimped into the cartridge and no one offers any service parts.
For me, the compression valving made it into a different bike.