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.


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.

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

  • Similar Content

    • By Mikeybabbel
      Hey guys, I just picked up a running 03 yz125 a few weeks ago and upon tearing down the top end, I noticed the cylinder head looks a little beat up. Is it possible to just clean it up or am I better off just buying a new one? Thanks guys. 

    • By faizakhtar125
      Hey guys I just bought a bike last night. So the seller said the bike will turn on but then die. We didn't try it because it was really late at night and it was raining (seat was wet). But he said if you bump start it, it will turn on and ride. So what do you think the problem is? I just want to make sure it runs... I probably won't be able to bump start it till Saturday (rain)... It's a four stroke, and I know absolutely nothing about them. Thanks.
    • By neonmarine
      Hey guys, 
      I've used this forum as a "guest" for awhile now and I thought I'd share my build now that it's all coming together.  The primary purpose of this project is to help me train for roadracing my 2009 R1 at lower speeds as well as giving me a cheap alternative to racing the big bike. 
      Here's what she looked like when I picked it up from a local shop.  Paid $800 cash for the bike as you see it with 17' rims, FMF pipe, EBC 250mm front rotor and clip on handle bars.

      Fits PERFECT!

      Shake down run at the Herrin Compound last summer:

      As she sits today:

    • By 125 yamaha guy
      i bought my yz125 from a dealer and they said that the clutch was broken so i bought it and it worked fine it would run move and everything and then it started to act up and now only first gear works barely though. when you put it in first it acts like its bogging down but its not and when you go into gears 2-5 it wont move i dont know whats wrong with it im assuming the clutch is slipping or something if you know please leave me a comment