KX125 85-86-87

I chose an 83 to do the same thing you plan on for your bike. I stared out planning on new tires and chain and sprockets. That turned into a winter long project of doing everything that cab be done to a bike and selling two other bikes to fund it
I like the early KXs because there aren't many out on the track.
The early electro fusion cylinders were not the best. Mine had low hours on it and its being replated.

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I beg to differ on the motor of the 86'. It was pretty damn fast - faster than the 87', but it was all top-end power. It was hard to ride fast on a technical track, but nonetheless, it was a fast motor. I had both an 86' and an 87'. The 87' was easier to ride because it had a wider, smoother powerband, but in a long drag race, the 86' would kill it.

Former owner of '85 and '86 kx125. The 86 felt more refined as a whole and looked pretty high tech at the time with the first in class rear disc. 86 had a top end motor. 85's motor was bottom/mid and hit pretty hard. I found the 85 easier to ride and faster.

My 86 had cracked rims after a while. The plastic was brittle on both bikes.

Can you post up some pics of your '86?

I owned a '85, '86 and an '87 KX 125 and in my opinion the '86 was by far the best of the three. I broke several frames on the '85 and several rims. My '86 was full DMC motor mods and that bike ripped. The '87 was fast but had super soft suspension and had to be resprung. The '86 KX 125 is in my top three of favorite bikes that I ever owned.

I too owned many 1980's KX 125ers....had the '84, '86, '87, and '88 models. Here is my '86 with some DMC stuff (pipe, oval silencer, etc) and it was the first year for the under the swing-arm, linkage Uni-trak rear suspension. I loved the bike's handling and remember it was a little soft suspension wise, but the biggest problem I had was getting it jetted properly. It had an annoying bog sometimes off the bottom, and I wasn't smart enough to figure it out. Anyway, my favorite of all of them was the 1987! PS. Note the home made bike stand my buddy made for my in shop class! Oh how cool MX was back then!

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MXM...you are killing me with that bike! If I wasn't married, and didn't have three kids and 5 motorcycles in the garage....I would buy that from you right away! Awesome job my friend!

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Hey guys! I'm 14 and just bought a 1987 Kawasaki kx125 project and need some help. The engine most likely needs a motor swap, it seems almost impossible to find a '87 motor but there are multiple other year motors, my question is what motors are compatible with the 87' frame with little to no fabrication or mods.

If you still have the cylinder/ powervalve setup for that bike, it will be more cost effective to rebuild that motor.
Being 14 though, makes me have my doubts that you will do this...
The 87' was physically the same motor as the 85' and 86', but they had a single downtube frame so the exhuaust exited out the side instead of in the center. So your pretty much stuck with an 87' motor in that frame.
Rebuild it if you can.