91 KDX250 fork question

[fatty_k]

A buddy of mine is just getting into riding, and we found a 91 250 that seems to be in excellent shape. The one thing that concerns me is the forks. He has the reciepts that show having the fork seals replaced by a local shop. But there is a problem I think. When the bike is standing up on the kickstand, the forks sag about 3-4 inches, and when I pull up on the front end, the forks rise up. When I comressed them, they compressed fine, but did not rebound back to normal ride height. They returned to that position with about 3-4 inches sag. I am guessing that there is a lack of oil in them. I know they should have some sag, but these forks just dont have any rebound and a lot of sag in them. Any ideas of what might be wrong with them? He really likes it, and I think it is a nice bike except for the forks. BTW, they are inverted forks on this model.

 

[Matt90GT]

First off stock they have really soft springs. in the .34 range. Being older they could easily be sagging since they are so soft to start with.

Second, there is no rebound adjustment. They have a very stiff rebound. If you use anything thicker than a 5w fork oil, they will not come back up and be very slow to rebound. This is probably what is going on.

You can either get aftermarket springs for them or get some KLX springs. They are 43mm units, but the inside fork spring guide is bigger than what is used on the conventional forks (you cannot use the XR springs in them). The KLX springs are a .38 rate but are a bit shorter. Thus you can find a valve spring off a 302 Ford cylinder head to make a second spring and make it progressive. This also makes the springs longer so you dont have to use a taller spacer. Cheap way to fix things, but works well!

I good revalve on the forks would be a good idea. I have not gotten that far yet as I have the forks working really well.

Other maintenance items on those forks are to install the motionpro fork bleeders. Also purchase new fork wipers with new seals! If you do not keep good wipers, you are going to get dirt in the seals and cause leaks. The Seal savers are one of the best things you can install on those forks!

 

[fatty_k]

Thanks a lot. I think if/when he buys it, we will change the oil and possibly buy heavier springs.

 

[dirt bike dave]

It sounds like the particular bike described above does not have any preload on the fork springs, and/or the springs are too short. The owner may have done this itentionally to lower the front end for quicker steering in the woods - the bike has slow steering geometry.

As Matt says, the stock springs are way too soft on the 250. Like the other KDXs, Kawasaki chose to use soft springs and too much high speed compression damping. The result is harsh forks on sharps hits like roots and rocks but weak springs that are too soft on big hits and whoops. Worst of both worlds. The bike will be vastly improved with the right springs and a revalve of the forks.

I really liked my old KDX250 but the stock forks were grim. I put in stiffer srpings 0.41kg/mm, I think, and used Race Tech Gold vavles. based on my friend's experience, we used less high speed compression damping than the RT charts recommended and a little more low speed damping. Worked pretty good.