How much compression does yz 250 need?

I have a 2006 yz 250 starts good but seems to be sluggish in the power range I just did a compression test got 165 psi is that good or bad how much should the range be?

Over 200psi

That should be enough compression to run fine. Check the compression when the bike is hot then again when cold. See what the difference is. If it drops more than 25psi I would re ring it.

My stock motor with 60 hours on piston and rings had 180psi (cold). This was with 12mm of the top ring missing and a damaged power valve and cylinder wall. Bike ran fine on trail rides but overheated often in races and gnarly Hill climbs.

I would think 165 would be pretty well shot.

-E

Also 165 psi was cold would psi would be lower when engine is warm?

As a comparative, my completely stock YZ125 gets about 185psi on a fresh top end / OEM cast piston.

 

200-220psi should be about normal for a healthy 250.

Edited by mlatour

You'll get a bit higher readings when taken warm,

don't forget to hold the throttle wide open and hold the kill switch when cranking it over.

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