89 framed Hybrid, air cooled motor

[arjay200]

My guess would be an early 83-85 KDX engine would fit. Maybe the 86-88 engine. I'd use Ebay crankcase/bottom end pics to get a better sense of it. Compare the 84 KX125 crankcases with 84 onwards KDXs. It's always going to take a bit of work - cutting new front mounts and head stays at the least. Main thing is that the back of the engines are the same layout. Good luck, it would be a cool build.

[Tyl3r]

Sweet ride, just saw this now! How is she running after the dyno tune?

[arjay200]

Thanks! The dyno run topped out at 22 hp at the rear wheel. With a mid range lean spike that we couldn't jet out. There's also detonation under load at high revs when riding on the dirt (didn't show up on the dyno bench). I just found out there was a mismatch between the E series manifold and the C series reed block. The two apertures don't line up (with potential sealing issues). The E series manifold mouth is offset, C series reed hole is centred. So I've put in an E series reed block and am hoping this was the issue.

[Tyl3r]

Nice, that's awesome that you have a dyno at your disposal to help with the fine tuning. How did you find out about the reed block issue? I only have experience with the H series bikes

[arjay200]

This mismatch. Just found it by accident when servicing the top end.

[Tyl3r]

Ah, gotcha, yea can visually see the difference there.