bogging; fouled plug after rebuild

Sort of a rebuild. Just a piston ring.
Anyway, i got it all together, put it through one heat cycle, it ran fine. I thought it was cutting out a bit, so i turned the air screw out to ~2 turns. Let it cool for about 1.5hrs, go out to start it again, it warms up good and idles fine. As soon as i hit the throttle, BOGGGGGG. Trying it again a few times, the same bog. The last time it bogs down and won't start again. I checked the plug, definitely wet.

What could be the issue? I think my jetting may be a little rich after the rebuild, it was probably jetted for the worn top end. Here are the specs, tell me what you think.

'94 CR125
FMF Fatty
175 main; 172 stock
55 pilot; 58 stock
1.5 turns out
40:1 mix
2 from the bottom on the needle

Thanks guys! :ride:
:BS: ^&%*&* you guys !:lol: Goes to show ya what I know!:smirk: Our Kx100 had one.but I don't know about that old of a POS.:P Kidding:thumb:

For All I know you put your piston in backwords or left a rag in the airbox.:prof:

:lol: good luck though! :thumb:


Staff member
Have you tried adjusting the air screw again? I adjust mine every time I go ride. Also is the gas fresh?
I just got a couple plugs, i'm going to go tinker some more. Could be the old gas, but it ran great the first heat cycle..I'm going to put the needle back to stock, mess with the air screw. I'm probably going to end up ordering some jets. 170, 172, probably up and down one on the pilot.

Correction: PO went larger on main, smaller on pilot. :smirk:
(no idea why.)

Anyway, I got a few new plugs, ran it around for about 20min, it ran great. Adjusted the air screw to about 1 3/4 out and it idles perfect. Took the plug out and it's a nice tan. There was a bit of a bog right off idle, but if you don't step on it it's fine. (also put the needle back to stock)