06 yz450f...... I Lost compression stroke

I feel no compression stroke while trying to kick start my bike.

Let me explain. My last ride was during a hare scramble in Oct of 09.

The bike ran fine aside from the fact that it started very hard while cold. I didn't have any problems with it all day before washing and storing it for the winter. Last week I ordered a new set of ice tires hoping to hit the ice on Sun.17th before this happened.

When starting a bike I always slowly apply pressure on the kick starter to move the piston up and down a few times "without trying to start it" , as if priming the motor before really jumping on it.

This time while slowly moving the kick starter down with my foot, I felt an obvious compression stroke. After 3 more slow and controlled kicks "only applying little pressure on the kick starter", I felt what I assume was the power stroke, the exhaust stroke, and the intake stroke without ever feeling a compression stroke again after that.

Is a valve stuck open, closed, carboned?

Is it the Auto decompression valve?

Is a Shim cocked in place a little?

All opinions welcome, please help!

Thank you.

Edited by butek

I would check valve clearances if compression seems low.which you would feel on compression stroke naturally.plus it's a good baseline start to check off what it's not.


Is a valve stuck open, closed, carboned? Possibly

Is it the Auto decompression valve? No

Is a Shim cocked in place a little? No

It could also simply be that your valve clearance is low.

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