07 yz450f sometimes kicks with no compression?

Hey all,

I've been lurking around here for a while just gathering the loads of useful information you guys have been good enough to put up:worthy:. Anyway I have a 2007 yz450f and have had 0 problems, just change the oil, and air filter and ride. Have not done a top end, or had the valves shimmed. Ever since I have pulled it out this year I have had something odd happen each time I ride. When riding, if I stall the bike, when I go to kick it over sometimes it will kick straight through the stroke with no compression. Then I'll slowly kick it until I get compression back and it will start up right away.

So my question is what do you guys think is the problem? The bike doesn't lack compression other than when this occurs and my first guess would be that a valve is sticking open allowing air to pass by and not be compressed. I have not checked for valve clearances mainly because the bike has never given me problems starting. If anyone could give me some guidance as to what exactly to look for I'd appreciate it!

bump! anybody have some advice?

Wouldn't hurt to check the intake valves...they tend to tighten up over time. If they are too tight especially when things are hot then the valves wouldn't "seat" completely and you might lose compression.

Could be a sticking valve or carbon deposited on the stem or valve head. See if a bit of fuel injector cleaner added to your gas doesn't help it. (read the label for the mix rates)

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