New KDX250 rider, restoration.

[wayneh]

Hello everyone. A couple of weeks ago I picked up a 94 KDX250 on a whim for little money. Here's a pic from the ad,
and one from the almost finished product. I have new fenders on the way. I am very pleased with the power and grunt of the bike and the rear suspension works fine.....the forks however. I see through a bit of research that 91-98 KX forks appear to be the same tube size and seem readily available for good prices. Anyone have experience with KX125 or KX250 forks on the KDX250. Seems like a no brainer to bolt them onto the current triple clamps and have both compression and rebound adjustments. Or have I missed something. Any input would be greatly appreciated.

Thanks, Wayne

 

[Tom68]

I think your on the right track with later forks, you'll struggle for springs for yours the ones that fit require you to machine down the nylon inner guide, also may coilbind and if you do the stress calculations they probably won't come back to free height the genuine ones didn't.Read somewhere once that early 90's KX250 can break rebound rods, don't know if they come apart then and hope it doesn't apply to my KDX, so later will be better, they could do with a better front brake as well.

 

[wayneh]

Thanks for the info Tom. Any ideas as to whether the KDX250 axle and wheel will works with the 91-98 KX forks? I am trying to match up part numbers from the Kawasaki site but find myself going around in circles.
It took a bit of getting used to the height of the bike (I'm only 5'7") but after cutting and recovering the seat it's much better. I have gone through and replaced the swing arm bearings, cleaned and greased the pivot bearings (they will probably need replacement next year) replaced the rear wheel bearings and a few other small pieces. the frame received a fresh coat of paint and all in all the bike looks and runs pretty good. I originally bought it thinking I would clean it up, get it running and resell it for something a little smaller and newer but I find I am getting to like the old girl!

 

[glad2ride]

Congratulations on the bike!

1991 - 1995 KX125 - KX250 and 1991 - 1996 KX500 tubes will fit into the 1991 - 1994 KDX250 clamps. However, to keep it a bolt on operation, the KX axle and front wheel ( and brake system, depending on year) will also need to be changed. The MX forks will be valved (tuned or set up) for MX, not trail riding. No matter which set of forks you go with, the correct spring rate for your weight is needed. On the KDX250, a switch to a modern stiffness fork spring will require the spring guides to be shaved or ground down a little, as was mentioned by Tom68. I haven't heard of any coil binding, but haven't ridden a set either. The 93 - 95 KX style springs will work. A small spacer is needed to take up the gap.

Good luck with it, no matter which way you go. You may want to try changing out the fork oil, then consider the correct rate springs for your weight. Stock is .35 Kg/mm rate, which is considered very soft now. Check the www.racetech.com site for a recommendation for your weight.

 

[wayneh]

glad2ride, thanks for the info. The problem with the KDX forks lies not in the springs as I am light at just about 150 lbs but the compression damping is absurd! Over larger bumps the forks work ok but on smaller stuff you can feel every nook and cranny! At the cost of replacing the valves and springs I was thinking that a switch to KX forks might be a viable option which would also net me rebound adjustments as well. If I can find a bolt on solution i.e. using the current triple trees ( and brakes if possible) that would be the simplest. Thanks again for the help.

Wayne

 

[glad2ride]

You are welcome.

The stock springs are too soft, even for you at 150 pounds. Race Tech recommends a .406 (closer to .40 Kg/mm rate). In the early 90's, it seems that softer springs and stiffer valving was the norm. Modern thinking is using a stiffer spring. It will keep the forks higher in the stroke and not allow them to sag so much.

If you have not changed the fork oil, I assume it is very old and worn out. Otherwise, the bushings may be worn out, or a tube slightly bent, etc. which would cause binding, keeping them from working as they should.

Your current forks, or any KX forks you fit, will need a full rebuild to work as they were designed, as they will be around 15 years old. That many years of use in a harsh off-road environment causes the internal parts to wear out.

A set of MX forks will not be valved (tuned) for rocks, roots, ruts and such, since those are not on a MX track. You probably won't be doing any big doubles or sky jumps out on the trail either. The KX forks may come with a spring rate that is closer to what you need.

Having adjustable rebound is not something to consider a huge plus compared to having the correct spring rate.

You may want to look at the parts diagrams on the Kawasaki site. I think the brakes are the same on 1991 KX's, but then may have changed (at least part numbers) the next year. I am not sure if the newer year brakes mount the same or not. You might be able to swap some parts around to make it work. (this caliper mount, that caliper, this hose, etc.)

Where the axle mounts to the forks, there is a big difference in the mounting style, axle diameter, etc.. which requires the use of the KX axle (and wheel) to keep things simple. One could have an axle made at a machine shop, but that goes beyond "simple bolt-on" in my opinion. One could have any part made, but the cost is a lot different than hopping on eBay and buying used parts.

If you go with the KX forks and wheel, the tripmeter / odometer drive won't work with them, if that is something you need.

If you decide to get KDX or KX forks rebuilt, revalved for your weight and riding style, plus buy the correct rate springs, (kind of an "all things being equal" and functioning as they should), the KX forks will be more modern and are technically capable of a higher state of tune due to the internal construction with more advanced parts, R&D applied, etc.

Look around on the internet for pictures on how the KX wheel mounts, if it is not making sense as to why it won't work.

Again, congratulations on the bike. If you have a few more pictures, please post them.

 

[Tom68]

I'm 160 lbs, first time I bottomed the standard forks they lost free length (only had to grab the brakes on ashphalt, also ripped valve stem from tube so I fitted a rimlock) they now fit with no preload and since I'm too cheap to buy springs I run them with air pressure which is good enough for what I'm doing. You won't be able to get enough preload on std springs. I have no problems with original valving but it should have more rebound to cope with the air. Looks like glad2ride has you covered on interchangability.

 

[glad2ride]

If the stock springs fit with no preload, then it may very well be time to replace them.

The 997 series Eibach springs, which are no longer made by them, gave 10mm of preload with no spacers installed. The distance inside the forks from the top of the cartridge seal head to the bottom of the fork cap is 490mm. The 997 Eibach springs are 500 mm. 10mm is the recommended amount by Race Tech. The currently available springs are around 484mm, or so, requiring a spacer to be installed (along with the spring guides being modified to have a smaller outer diameter. As the fork spring rate increases, two variables do not change. The length stays the same. The outer diameter stays the same. The thickness of the coil wire gets larger, which in combination with the outer diameter staying fixed, the springs inner diameter shrinks, rubbing against the fork spring guides. They are $10.something each at www.ronayers.com, so if you are tinkering and do not want to mess up the one current set you own, a new set can be purchased, then the old set modified. I used a bench grinder, then hand file, then sandpaper on the set I modified.

 

[cash_62]

Hey, great looking resto job! I'm in the process of giving my 95 200 a facelift and looking forward to posting pics soon!

 

[Tom68]

If the stock springs fit with no preload, then it may very well be time to replace them.

The 997 series Eibach springs, which are no longer made by them, gave 10mm of preload with no spacers installed. The distance inside the forks from the top of the cartridge seal head to the bottom of the fork cap is 490mm. The 997 Eibach springs are 500 mm. 10mm is the recommended amount by Race Tech. The currently available springs are around 484mm, or so, requiring a spacer to be installed (along with the spring guides being modified to have a smaller outer diameter. As the fork spring rate increases, two variables do not change. The length stays the same. The outer diameter stays the same. The thickness of the coil wire gets larger, which in combination with the outer diameter staying fixed, the springs inner diameter shrinks, rubbing against the fork spring guides. They are $10.something each at www.ronayers.com, so if you are tinkering and do not want to mess up the one current set you own, a new set can be purchased, then the old set modified. I used a bench grinder, then hand file, then sandpaper on the set I modified.

Must be another difference with the Aussie KDX250F Zero preload for my forks is 455mm, no surprise other differences include different primary drive ratio, some gear ratios,balancer shaft, steel tank, oil injection (the reason I'm keeping it), steering column lock and no exhaust port timing valve just the drum valves which leaves the bottom end a bit weak but I fixed that with a Gas Gas 300 piston.

 

[glad2ride]

Yes, the SR version is a bit different from the dirt-only model the original poster has.

 

[wayneh]

Thanks everyone for the replies and information. You guys are awesome! I agree it is probably time to take a look at the internals as I am sure some attention is needed. At the very least a drain and refill of the fork oil which I am sure the previous owner neglected. Anyone have a downloadable description of the dis assembly and service procedures for these forks?
The decision I have to make is whether to put the $ into this set or upgrade to the KX style forks. The general consensus on this and other KDX forums I have browsed seems to be that the KX forks are worth the effort however most of the applications have been aimed at 200s and 220s which are a little bit of a different animal. Tom, you mentioned running yours with air pressure. Have you installed schrader valves the fork caps? An old trick we used to do in the 70s which I had done on my Penton ISDT bike. Ahh those were the days twin rear shocks laid down and a whopping 7" of travel!
I'll get some more pics up for you guys this weekend. Thanks again for all the info.

Wayne

 

[glad2ride]

The KDX250 supplement manual is copyrighted and only $15 or so at the dealer. The base manual is needed for most other tasks that are similar to the 1989 - 1994 KDX200 models.

 

[Tom68]

1/8 npt pushlock fittings in fork caps drilled ctr on top drill intersecting passage from underneath, plastic schrader tee for filling, fork oil at 125mm no higher or you'll end up with ridiculous bottomed pressure. Have had some hard landings with 15psi bottomed and created no problems ran at MX track last weekend with 17psi no problems also ran 20psi for a big tabletop that I was coming up short on. Best part is, to run on the oval I just let the air out. Have an XR500 with 37mm forks and will set them up for 25psi or more.

 

[Matt90GT]

dont waste a dime on the stock KDX250 forks. They have no rebound adjustment and the valving is not good at all.

the KX forks 91-95 is what you want. much more adjustable and have rebound adjustment also. They are 10x more plush than the KDX forks with the correct springs in them and new fluid. .42 kg springs is what I ran in them, then used the stock KDX stem pressed into the KX clamps. Also run the KX front wheel and brake assembly to make things easier.

1990 kx rear fender will bolt up pretty easily to the bike

Jetting is way off from the factory. Use a 26" headgasket (88-91 KX, raises compression), then this is the jetting I ran on my bike (aftermarket exhaust): Jetting: 38/158 , R1367H needle 3rd clip from top, #6 slide (sea lever, 50:1 mixture and premium gas)


That is a lot closer to the KX jetting. Bike absolutely ripped 5th gear wheellies, great power with the WR gearbox. I was also running the Vforce reeds on the bike.

hope that helps

 

[wayneh]

Sorry I haven't replied, came down sick with food poisoning and haven't been to "lively" for the past few days! New fenders arrived and I have them installed. With a little trimming the KX rear went on fine and looks good. Picked up a good headlight shell on the auction site, now just looking for the actual headlight lens/housing as the one I have is badly cracked. I did score a set of 95 KX forks that are supposed to be in very good condition really cheaply and a front wheel, rotor and axle. When they arrive we'll have a go at putting real front suspension on this beast. If I can get that sorted out I think it will make a great bike and I look forward to getting some riding time in. I'll post some more photos as the project progresses and let you all know how it works out. Thanks again everyone for all of your help and advise. This is a great forum, I find myself here at least once a day and am working through the 500 some posts here. What a wealth of information on these bikes!

Wayne

 

[glad2ride]

Cool, on getting the 1995 forks!

Before you take off the old forks, measure from the ground up to a few points on the bike.

You want to make sure that after the new forks are installed that you are not riding a chopper or a stinkbug. :-)

 

[wayneh]

Alright! Got the KX forks, front wheel and axle. The forks bolted into the triple clamps without a problem (remember this is a 94 KDX250 which came stock with inverted forks). Unfortunately the caliper will not bolt up, but I was able to cop one from the auction site reasonable, should be in in the next couple off days. The forks were in very good condition, straight and unmarked sealing surfaces. They do need seals but that is to be expected buying used suspension parts. took a couple of test laps (carefully as no front brakes) and so far see a definate improvement over the KDX forks. I am sure with new seals and oil and a little setup time these will work out nicely. Thanks again for all your help and advice. Now both ends of the bike work together and the bike is much nicer to ride over sharp edged bumps and steering and handling are much improved. I'll get some pics up this weekend if the weather cooperates.

Wayne

 

[glad2ride]

Sweet!

If I helped any, then you are welcome. Be sure to post again when you get it fine tuned.

 

[wayneh]

You did indeed help, the information that was supplied made tracking down the right parts much easier. The front end is working much nicer now...the bike actually turns! I have new seals on the way and will be rebuilding the forks when they arrive. All and all I am very happy with the results. Here's a few photos of the bike and a couple from the test ride after the fork install and a change to a 14/49 sprocket combination. Thanks again for all the help.

 

[glad2ride]

Look, Ma! No brakes! :-)

It is coming right along.

 

[wayneh]

Got brakes now! Had a tough time getting the fluid to the new caliper. Finally had to resort to a vacuum pump to get the fluid through the line and the caliper. After bleeding the numerous times have a good solid pull at the lever. Fork seals are hear so this weekend may be time to pull the forks apart, replace the seals and new fork oil. Anyone know a good starting point for oil level?

Thanks, Wayne