Need help with harsh forks

[andrew]

I have a '96 KDX200 with the standard Kyaba forks. I replaced the soft OEM springs with a .41 set for an XR400, which has been a huge improvement.

My problem now is that while they are awesome on heavy stuff like jumps etc, they are quite harsh on the small stuff like rocks. The springs I put in may be a little stiff for me (I'm about 90Kg fully kitted up) so I've tried to compensate by using a lightweight fork oil (ATF fluid actually),and made my compression setting as soft as possible.

What else can I do to make them a bit softer in the first part of the stroke? Would gold valve emulators make any difference? What about lowering the oil height? Another thing I was thinking about was drilling out the oil holes in the inner tube, although I am not confident in that without some good advice and direction on how much to drill out.

I suppose what I'd REALLY like would be a set of WP's or Marchozzi's :aj: , but that is out of the question at the moment! So, any advice y'all can give would be much appreciated.

Thanks,
Andrew

 

[dirt bike dave]

You need to reduce the high-speed compression damping on that fork if you want it to work well on rocks and roots. Basically, on a really sharp hit, the excessive high speed damping will not allow the fork to move quickly enough.

Lowering the oil height will allow the forks to bottom out more easily, but will not really change how quickly the fork responds to a sharp hit in the first part of the travel.

Lighter oil mainly effects the rebound damping, and will not make a big change to how the fork responds to a sharp hit from a rock or root.

The KDX needs the stiffer springs if you want it to handle big jumps and whoops, but even with the soft stock springs there is too much high speed compression damping on the sharp hits.

The Race Tech cartrdidge fork emulators are for the earlier generation KDX's with damper rod forks. Too soft springs and too much high speed damping is a characteristic of all years of KDX. I had the emulators on my '90, and they and worked wonders. I belieive your bike should have the more modern fork and would use the gold valve instead of the emulators.

I used the gold valves on a '91 KDX250 and they worked well, but based on a friend's experience, I used a shim stack that had less high speed damping and slightly more slow speed damping than Race Tech's chart recommended (with the gold valve they give you a bunch of shims and a chart to help you figure out which way you want to stack the shims). If you have a reputable suspension shop in your area, they may be able to revalve your forks even without a gold valve.

 

[andrew]

Thanks mate, there's some good info there for me to follow up - appreciate your help.

I believe my forks are the older non-cartridge type. There's basically a tube that runs up the inside of the fork leg. They are not at all like the cartridge system I have seen in USD forks.

Would enlarging the holes in that tube give the desired result on the first part of the stroke? If so, how much? I think I have read about this somewhere a long time ago, but not sure if it's the way to go. Anyone else ever done this?

Cheers
Andrew

 

[dirt bike dave]

Since you have the damper rod fork I highly recommend the emulators. They work great. However, you certainly could reduce high speed compression damping by making the holes in your damper rod bigger. Sorry, never done it, so no recomendatiosn on hole size.

As part of the emulator installation, you do greatly enlarge the holes in the damper rod and maybe even drill some new ones. The larger holes will have little or no restriction to oil flow. The emulator sits on top of the damper rod and controls the oil flow with a spring loaded plate. The spring is over a bolt and it is adjsutable by tightning or loosening the nut on the bolt. You have to remove your fork springs and fish out the emulator to adjust it though - your clickers will no longer work.

The emulators I put on my '90 KDX were one of the best peformance improvements I made to any motorcycle I've ever owned. Combined with stiffer springs and the right oil level, it made the bike worlds better than stock.

 

[Rhodester]

I have a '95 KDX200H (U.S. version). Mine has cartridge forks which I've put Gold Valves in. I find it hard to believe that a '96 KDX anywhere would have the old damper rod forks. Remember, just because they're not upside down forks doesn't means that they're not of a cartridge design. I believe that my '95 was not the first year that they put cartridge forks on the KDX (it was probably closer to '93).

 

[bikepilot]

I had a US 96 KDX200 and it definately had cartridge forks (conventional, 43mm inner tubes). I raced it in harescrambles and actually was very happy with the stock suspension. I weighed 150lbs at the time - the courses were typically, tight and littered with rocks and roots - standard east coast stuff:)

btw, ATF is usually 5-7wt. Stock fork oil is 5wt. It would seem that the fluid you are using is not lighter than stock (or at least what was stock on my 96KDX).

good luck

 

[dirt bike dave]

Its it possible someone swapped forks on the '96 with an earlier year, or perhaps the bike is an 'SR' street legal version that may have come with the old style forks?

 

[andrew]

No, I'm quite sure they are the stock forks; the description in the manual on how to strip them is spot on. I just wasn't sure if they are proper cartridge forks that would be able to be fitted with the gold valve, or an earlier style that couldn't.
Thanks for all your replies.

Cheers,
Andrew

 

[Robcolo]

Dual Personality

Therein lies the problem with {all} KDXs --they're two completely different bikes with just a change in spring rate. I've been trying for 2 years to design & install a dual rate front fork spring system. I'lm using the stock .35 springs for their great handling of the nasties --rocks, roots, ledges and then adding an air spring [upping the effective rate to .38 -.40] pretty much on the fly so the bike won't wash out when it gets up into 3rd gear & beyond. I'm using a sub-tank to keep the added rate more linear, a small pressure gauge and a mini bicycle tire pump to inject the air. The only real negative i'm finding is some increased seal stiction from running a positive pressure in the forks.

 

[andrew]

OK guys, I pulled my forks apart, and find it is a basic cartridge fork. I have spent all afternoon reading everything I can find on shim stacks. I have noticed almost everything refers to a tapered stack. Mine has a straight stack, 10 of 17 x 0.1 and a 17 x 0.2 on the bottom. From my research so far, I am thinking I'll take out 2 of the shims to give me a 15%-ish reduction in HSC. I know it will also affect my LSC, but with my clickers already wound all the way out I figure I can compensate a little by turning the compression up a bit.

Any opinions or ideas on how to do it differently? I know that to get it spot on maybe I should be betting RT Goldvalves, but I don't have the dollars at the moment! And besides, I'd like to experiment and learn a bit more by doing things myself!

Andrew

 

[marcusgunby]

You plan sounds good to me, that straight stack gives less hs and should work ok in woods etc.

 

[andrew]

Thanks Marcus, I've read more than a few of your posts from the past on this topic, and you seem to be fairly cluey about this stuff so I appreciate your reply; it kind of validates that I'm on the right track!

I put it back together minus two shims, and the fork already feels plusher just rocking it against the brakes - the real test will be next weekend when I go smash some rocks...just hoping two shims wasn't one too many...20% reduced HSC...well at least I can put one back in if I'm not happy!

Thanks heaps,
Andrew

 

[dirt bike dave]

andrew - good job doing it yourself. Honestly, I think with the right shim configuration your fork can work just as well as with gold valves. Even with the gold valve and Race Tech's recommended stack, you might find yourself pulling it apart again.

Go find some rocks and roots and a few jumps. Preferably, a secton you can ride over and over again to test on. If you are bottoming in the rocks, turn your clickers in and/or raise oil. If bottoming on jumps but fine in the rocks, try raising oil level a little.

With the clickers, remember that each click makes a bigger difference the further you go towards all the way in (i.e. the difference between 1 click and 2 clicks out is MUCH bigger than the difference between 11 and 12 out).

 

[andrew]

Thanks, DBD, it is a satisfying feeling to be able to research and then achieve the aim (with a lot of help from my forum mates !) without resorting to taking it to the mechanic.

I'll take those points of yours on board when I test it this weekend.

Cheers,
Andrew