KDX250 Fork Spring Source

I had a '91 KDX-250, with gold valves in the front forks. I put in 0.40 kg/mm fork springs and weighed about 190 when I had the bike.

IMO, the Race Tech calculator recommends too stiff a spring for your intended use (trail riding). I would suggest more like 0.41 - 0.42 kg/mm for your weight. I think 0.455 will be too stiff.

The KDX250 has slow steering geometry. So to improve cornering in the tight woods, you want a little bit of fork dive when braking into corners. Overly stiff springs will hurt this. On my KDX250, I set it up with no spring pre-load. You can also grind the steering stop tabs on the frame slightly to allow for a tighter turning, without hitting the forks on the gas tank. If you go down 1 tooth on your countershaft sprocket from stock, you can take two links off the chain and move the rear wheel all the way forward in the adjustment range. The bike will still be plenty stable at speed (especially if you have a steering damper).

You can probably order the springs directly from Race Tech. You may have to call, as many companies do not include the older, more obscure bikes on their websites.

If you like your KDX 250 now, you will like it a bunch more when you fix the forks! It's a really decent bike underneath, but Kawasaki did not do a good job on the forks and the jetting, as well as a few other set-up related items.

The bike has excellent low end power for a 250, and you can get even more with an '88 KX250 thin head gasket. There is a lot more info floating around out there on this site for your bike, but you might have to dig for it.

You can get the springs for a 1993 - 1995 KX125 / KX250 to work. You will need to grind the white, plastic spring guides that go on the damper rod. The inner diameter of the springs increases as the rate goes up, and at some point they will rub on the spring guides. You will need a spacer to take up a little bit of difference in the spring length. Eibach used to make a 997 series spring for the 1991 - 1994 KDX250, but they discontinued it several years ago.

If I remember correctly, we use to use the stock XR600 or XR400 fork springs on the KDX250s. Do some research there, but that is my memory.

But you are way better off swaping forks for the KX of the same vintage 91-95. Better valving and rebound adjustment to boot.

RT # 3949

I don't think .40 or .41 will be stiff enough. With the combined weight of the bike an rider, some .44 or .46 springs may be in order.

As a general rule, you want less high speed compression damping for rocks and roots. Most MX bikes have too much high speed compression in the forks to be optimum on the trails.

Even the KDX 200 and 250 have too much high speed compression for very sharp hits, and Kawasaki makes it livable with too soft springs, which are then horrible on jumps and big whoops.

BTW, a free way to slightly stiffen a spring is to cut a few coils off (make sure you don't cut too much off or you will get coil bind before full travel). You will need to lengthen your pre-load spacer if you do this.

ssaulnier said:

Is there another coating that would be better than anodize?

Click to expand...

Better in what way?
Anodizing is one of the hardest of all the aluminum coatings, but it is also costly. It will also allow the dissipation of heat better than paint or powdercoating.

For the KX250 forks, I would stick with OEM parts and modify the base valve stack for less high speed compression.

I replaced mine with a set of KX '94 forks, and of course a new wheel and axle to go with them, but even without setting the new ones up, they're a different world to the original!

You might want to search through the suspension forum for posts on others doing it. You might be able to get away with just removing a few shims instead of replacing them. Less shims = less damping (slowing down the oil)