Low compression Kx250f

Ok so I just finished timing my valves and now my bike has low compression and won't start. It has a brand new wiseco piston rebuild with less than an hour on it. I took apart my motor because it was backfiring, running bad, and somewhat easy to kick over. I shimed the valves, checked my clearances, and timed the valves as well. Now it's back together and it won't start and feels very light to kick over. What could be the issue?

Possibilities

... slipped camshaft sprocket. Meaning the sprocket has spun on the shaft, making the timing marks out of time from the cam lobes

... a problem with the piston or ring(s)

... incorrect setup - double/triple check your work wrt correct valve clearances and cam timing.

 

Piston and ring are only part of the equation, how many hours on the valvetrain?

 

Valves may be shimmed to spec but if the faces and seats are worn and not sealing evenly all the way around,

compression is lost when kicking the engine over.

If the same valves have been shimmed more than once, it's sign they've begun to recess.

Edited by mlatour
Piston and ring are only part of the equation, how many hours on the valvetrain?
 
Valves may be shimmed to spec but if the faces and seats are worn and not sealing evenly all the way around,
compression is lost when kicking the engine over.
If the same valves have been shimmed more than once, it's sign they've begun to recess.


Found the problem, the head was warped. Had a friend flatten it at his machine shop and the bike runs good now. However it backfires frequently.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now