Tech: Testing compression?

[RatherBriding]

I finally broke down and bought a compression tester. Read up on the

proper method for testing, warm engine, throttle WO, kick until gauge

reached max PSI. Have 2 bikes at home, both were bought used with

unknown history, so no baseline PSI to compare to.

Bike 1 is a '97 WR250Z (2-stroke) - got a reading of 210 psi, thought

that sounded pretty good, even higher than I expected.... does 210

sound close to spec? too high?? I have been hearing a little pinging on

hard acceleration, using 93 oct pump gas.

Bike 2 is son's "03 YZ85 - got a reading of 150 psi. This is low

compared to the WR, but I don't know how it compares to a healthy 85cc.

Anybody know what spec is on a YZ85?

Thanks for any help!

Bob S

[RCannon]

The numbers sound about right. I believe I am at a higher elevation that you are. I would kill to get 210 psi on my yz 250.

However, dont think this is the end-all do-all test of the pistons condition. Its not. We tested a 2005 CR 85 at 145 psi and thought things were fine. Less than a half tank later the piston broke. Odds are, we would have caught the broken piston had we rebuilt the top end like we should have.