1994-98 KX125 Info

I can't comment on the engines, but for the chassis:

94 43mm KYB's no mid valve, frame welded brake pivot tends to wear out, frames are like glass.

95 and 96 chassis basically the same, new removable brake pivot, 43mm KYB's with mid on the 95, 96 get 46mm KYB's. New front number plate in 96.

97 and 98 redesigned swingarm, wider pegs. garbage progressive stock fork springs, 3 rear wheel bearings.

Cranks can be difficult to find. Look to send it out for a rebuild.

If you have to be pre-96, the 97/98 dead giveaway is the fat swingarm. Anyone who knows those bikes can spot it from a mile.

A few yrs after I quit racing, I borrowed a 97 KX125 that had been raced the previous year at Loretta's (mod class). FC suspension set up for a kid 20 lbs lighter and light years faster than me.

I really liked the bike other than it was slower than a stock new 99 YZ125 by a large margin. Now this bike had a ton of hours and had been used as a practice bike since...so I have no idea how well they run.

I found it very stable and liked the ergos much more than my old 1993 YZ.

Id go a 96 if you can find it. Less flex 46mm forks and the mid valve which when setup properly is a great fork. Ive got mine working really well after I resprung and revalved it.
I also revalved the shock to 01 specs which works great also. But thats on the 97 longer swingarm though.
Couple issues on the 95 (my first new bike). The power valve actuator was changed to have a two step design. Sometimes the centrifugal force doesn't get the balls over the second step and doesn't open the power valves fully. 96 changed it back to the 94 smooth version. But you can just swap out the 95 for the 94 or 96 version.

95 also changed the linkage so it firmed up in the latter half of the stroke but it made it a bit too harsh. 96 changed back to the 94 linkage.

The drum power valves need to be matched to the ports. Mine was blocking about a 1/5 of the port and made a good difference to the top end when trimmed.

The FMF Fatty works very well to beef up the power curve and give a bit more top end.

Run a cr front master cylinder to improve the brakes. Even my 97 brakes which were improved were not as good as with the cr master cylinder.

Good luck.

Unless you have a plethora of 90's 125's available I would just find one in decent shape (hopefully). You can swap front ends between 94-98 no problem, so don't let the forks be a deal breaker. You can usually find a set on ebay needing seals for under $75. Also, if you bought a 94-95 you could run the 46mm front end, just use the old numberplate.

Motor wise, I understand the '94 had a decent mid-top powerband, although not very fast stock, but still rated a good engine.

The '95 had the 35mm carb and two-stage powervalve cup (as stated above)- slow and hard to keep on the pipe.

The '96 had a good low-end bark and decent midrange, but ran flat on top. Good holeshot potential on short starts.

The '97 runs a lot like the '95, hard to keep on the pipe.

Again, the '98 had the new cylinder but I don't know much about it.

Can you put a 1998 kx250 triple clamp on a 1994 kx250 frame?