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is a leaky cylinder base gasket a cause to lose compression?
Quick math is 14.7 x compression ratio of model year = psi of compression test. That gives you a good estimate, but not exactly what you need, hence why you need to get a base from both compression ratings. My '06 YZ125 has a compression of 8.6:1 - 10.7:1, which equals out to 126.42 psi - 157.29 psi.
I think you have a bad top end all the way around. A new top end (piston, rings, wrist pin, etc.) and gaskets will run you around $125-$150 depending on where you get it. I would not be surprised to also find that your cylinder has a bad taper and/or out-of-round as well causing a ring to fit bad. What year is the YZ250?
whats up guys new to the site I have a couple questions this bike that I'm looking at to buy is a 94 yz250 but the guy wants $250 for it and it needs a transmission plastic and a top end what should I do dont know anything about yamaha's need help please????
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