Fork valve mod

[kdxdazz]

Wanted to share my fork valve mod, won't be able to test it for another 2 months, my theory is increasing oil flow to greatly reduce compression dampening, I've tried the valve shim mod and find it completely ineffective on sharp hits and rocks, anybody tried this? Please don't say just buy gold valves unless you want to buy them for me

[Slick_Nick]

I could see it working if you built the shim stack appropriately to compensate for the larger ports.

[kdxdazz]

I could see it working if you built the shim stack appropriately to compensate for the larger ports.

What are your thoughts on the shimstack, I was thinking put all 10 Shims back in

[KDXGarage]

Cool. Let us know how it turns out.

[Slick_Nick]

You’ll need to go much stiffer on the low speed compression stack in order to have the same damping for sure, and since the rebound stack is on the backside of the piston you’ll also need to stiffen that stack up quite a bit. Putting the stock shims back in I reckon would leave you with almost no rebound damping. Are you going to switch to a two stage compression stack?

[KDXGarage]

The rebound piston and damping is on the end of the damper rod, inside the cartridge. (not on the compression base valve)
There is no way to have a dual stage stack on the stock piston unless one custom makes shims. The only commercially available shims are the same diameter as stock.

I would put the stock quantity of shims on there to eliminate one variable. The only thing you are needing to test is how do the larger holes work.

[Slick_Nick]

The rebound piston and damping is on the end of the damper rod, inside the cartridge. (not on the compression base valve)
There is no way to have a dual stage stack on the stock piston unless one custom makes shims. The only commercially available shims are the same diameter as stock.

I would put the stock quantity of shims on there to eliminate one variable. The only thing you are needing to test is how do the larger holes work.

Ah you are right. Its been ages since I've been into the stock forks! This base valve should have the compression stack on one side and a check plate and spring setup on the other.

[KDXGarage]

Yeah, compared to the last 30 years, it is an oddball setup. They are nearly identical to 1988 KX forks, so I think they just copied them in design. I don't know about the valving, just the design.

[kdxdazz]

as i understand it the kdx forks are not a true shim stack anyway as the shims don't flex like a shock shim stack, they just open up and separate as the oil flows through, i went all the way down to 3 shims and the forks were still deflecting off of rocks, the compression clickers effect mostly low speed dampening right? for the single track riding i do i want to have it set up so if the clickers are all the way out the forks have very little compression dampening, the loops we do vary from 7 hours to 5 days in Thailand so you can imagine how exhausted i feel deflecting off of everything, i only weigh 63kg, i'm using 0.32kg fork springs and 2.5w motul fork oil. my ultimate goal is to get my 43mm showa forks from a xr400 bolted on but right now i don't have any room in my suitcase to take them back to thailand so these base valves are more of a stop gap, ive done the same mod on the xr400 forks and if they don't work i will bite the bullet and buy gold valves
i still don't quite understand what the small valve is and how it works, does oil flow down it and into the base valve or up and through it back in to the fork tube, could somebody elaborate please

[Slick_Nick]

You need to go stiffer on the compression stack, especially since you hogged those ports out. You’ve basically left yourself with very little compression damping, so you’re riding way too deep in the stroke and it’s going to be harsh. Get that stack stiffened way up, and get some proper springs for your weight, and you’ll ride higher in the stroke where the forks will be compliant.

[kdxdazz]

You need to go stiffer on the compression stack, especially since you hogged those ports out. You’ve basically left yourself with very little compression damping, so you’re riding way too deep in the stroke and it’s going to be harsh. Get that stack stiffened way up, and get some proper springs for your weight, and you’ll ride higher in the stroke where the forks will be compliant.

0.32kg are the correct weight springs for my weight and the sag numbers reflect that, I made my own preload spacers to get the correct sag,my other kdx has the stock 0.36kg springs and it's also harsh, many and most also complain of the harsh compression damping,. I have a yz125 spring on the rear which is 4.6kg but I have a 4.2kg spring in my suitcase to be fitted, rear is also terribly harsh but after studying about shim stacks I now realize I made a bad judgement on the shim stack I put in

[Slick_Nick]

You need to go stiffer on the compression stack, especially since you hogged those ports out. You’ve basically left yourself with very little compression damping, so you’re riding way too deep in the stroke and it’s going to be harsh. Get that stack stiffened way up, and get some proper springs for your weight, and you’ll ride higher in the stroke where the forks will be compliant.

0.32kg are the correct weight springs for my weight and the sag numbers reflect that, I made my own preload spacers to get the correct sag,my other kdx has the stock 0.36kg springs and it's also harsh, many and most also complain of the harsh compression damping,. I have a yz125 spring on the rear which is 4.6kg but I have a 4.2kg spring in my suitcase to be fitted, rear is also terribly harsh but after studying about shim stacks I now realize I made a bad judgement on the shim stack I put in

Correct springs for your weight according to who? Unless you’re 120lbs or less, those seem awfully soft to me.

The stock H series forks are some of the most plush I’ve ever ridden in the woods. Haven’t had them in probably 15 years, but I remember them being super soft on all the roots, rocks etc. As long as you’re going slow. Feed in any sort of speed and they were garbage though, that’s why most of us swap them out.

[MoonStomper]

If your front to rear spring ratio is out of balance for your weight, your forks will not perform correctly. You need the rear spring to be correct for your weight first. Then set the sag, compression and rebound for that rear spring. Then start with your forks. It’s all about balance or you will overdrive the weaker component and handle like trash.

Check out Race Tech’s suspension guide online.

[kdxdazz]

If your front to rear spring ratio is out of balance for your weight, your forks will not perform correctly. You need the rear spring to be correct for your weight first. Then set the sag, compression and rebound for that rear spring. Then start with your forks. It’s all about balance or you will overdrive the weaker component and handle like trash.

Check out Race Tech’s suspension guide online.

What makes you think the spring combo I have is out of balance?
Racetechs spring calculator is completely wrong when it comes to 60kg bodyweight and corresponding sag, has been for the last 3 bikes I've owned

[kdxdazz]

You need to go stiffer on the compression stack, especially since you hogged those ports out. You’ve basically left yourself with very little compression damping, so you’re riding way too deep in the stroke and it’s going to be harsh. Get that stack stiffened way up, and get some proper springs for your weight, and you’ll ride higher in the stroke where the forks will be compliant.

0.32kg are the correct weight springs for my weight and the sag numbers reflect that, I made my own preload spacers to get the correct sag,my other kdx has the stock 0.36kg springs and it's also harsh, many and most also complain of the harsh compression damping,. I have a yz125 spring on the rear which is 4.6kg but I have a 4.2kg spring in my suitcase to be fitted, rear is also terribly harsh but after studying about shim stacks I now realize I made a bad judgement on the shim stack I put in

Correct springs for your weight according to who? Unless you’re 120lbs or less, those seem awfully soft to me.

The stock H series forks are some of the most plush I’ve ever ridden in the woods. Haven’t had them in probably 15 years, but I remember them being super soft on all the roots, rocks etc. As long as you’re going slow. Feed in any sort of speed and they were garbage though, that’s why most of us swap them out.

a quick search will bring up many countless stories of harsh compression damping thats why the shim stack mod is often mentioned, the yamaha ttr250 uses the same forks but comes out factory with 5 shims
as i understand it all e series and SR models use the 0.32kg forks springs, to say that kawasaki sold a bike worldwide with springs that only suit 120lbs (54kg) or less is not logical, basically male humans weigh much more than that even in asia, maybe your forks had already been modded to make them more plush.
i have a completely stock kdx h series in my shed,forks are stock everything, i ride it and its very harsh for slow technical single track, the same or similar to my kdx220sr, over the last 20 years i've had many people give me advice on suspension set up, guess how many of them weighed 63kg, yep, not one

[SS109]

What makes you think the spring combo I have is out of balance?
Racetechs spring calculator is completely wrong when it comes to 60kg bodyweight and corresponding sag, has been for the last 3 bikes I've owned

Their recommendations have been dead on for me and I run between 138-140lbs (62.5-63.5kg). I normally run .38's up front and 4.8 in the rear and that was on stock suspension as well as forks that are way stiffer and harsher in stock form than the factory KDX forks. Hell, I have .40's on my KDX220 due to me being worried about the tire catching the fender since I didn't internally shorten them, and they have even been a good match for me as well.

[kdxdazz]

You are right I tweaked the racetech calculator and put in that I was over 45 years older and 60kg as that's my true weight . It came back as 0.34 front and 4.5 kg rear which is not that far off what I have on now, I just prefer a touch softer as majority of my riding is 1st gear single track, why are people trying to convince me my springs are wrong even though it's what racetech recommends and my sag numbers check out, my compression damping feels harsh even all the way backed out, again people trying to convince me it's not, I have no idea if my valve mod is the right thing to do and it could be completely wrong but I don't think anybody else knows either, if one thing is done differently on kdxrider that hasn't been done the same way for the last 15 years then people get up in arms

[KDXGarage]

time to spend the big bucks!!

Buy a zip tie. Put is losely snug on one fork tube, then hit some local trails right quick. It will let you know just how deep into the stroke the 0.32 springs, enlarged ports and thinner oil are allowing the forks to go.

[KDXGarage]

You are right I tweaked the racetech calculator and put in that I was over 45 years older and 60kg as that's my true weight . It came back as 0.34 front and 4.5 kg rear which is not that far off what I have on now, I just prefer a touch softer as majority of my riding is 1st gear single track, why are people trying to convince me my springs are wrong even though it's what racetech recommends and my sag numbers check out, my compression damping feels harsh even all the way backed out, again people trying to convince me it's not, I have no idea if my valve mod is the right thing to do and it could be completely wrong but I don't think anybody else knows either, if one thing is done differently on kdxrider that hasn't been done the same way for the last 15 years then people get up in arms

Do you know the Yamaha YZ250X or WR250 as it may be called in Australia? It is several pounds lighter than a KDX. Guess which rate springs it comes with? 0.44. How is a heavier KDX not going to come with springs at least as stiff as a lighter bike?

Springs are used to keep the weight of the bike and rider up. Check out spring rates for street bikes... 0.75, 0.80, and up.

What amount of preload are you running on those springs?

I am with the Canadian Terror, I think you are riding too low in the stroke when you hit the next rock or bump, so you are getting the feel of the stiffer part of the spring.

[MoonStomper]

I didn’t say your springs ARE wrong, I said IF… start there is what I’m saying. Always make sure the springs are rated properly for your weight and riding style FIRST. Then if you still aren’t loving it don’t be afraid to experiment. Fact is the KDX is notorious for having soft forks, which causes problems for a lot of folks trying to find the right settings.

I have no idea what your valve mod will do, but it will probably change something!

My suspension guru installed Belgian valves in mine (he says they are like the Gold valves but better for the KDX forks). We went up a size on front springs (Racetech), and did some other black magic and secret chantings. All I know is that my bike isn’t trying to kill me in the sand whoops anymore.

He did say that the KDX rear spring has a wider range of adjustment so just because you go stiffer on the front you don’t necessarily have to change the rear, unless it ends up unbalanced. Just depends.