Compression

[Hank]

I did a compression check today and both cylinders were a 75psi. Is it time for a new top end?

[00sheerzr]

I did a compression check today and both cylinders were a 75psi. Is it time for a new top end?

ya i would say your alittle overdue for a rebuild, just make sure your using a good compression tester with a schrader valve in it and the fitting should be the same size as the sparkplug, 75 sounds really low i would double check that, do you have any trouble starting or running it?

[yamahaman244]

I did a compression check today and both cylinders were a 75psi. Is it time for a new top end?

 

ya that sounds really low usally when they are blow 100- or 90 its time for a rebuild just did my compression test after my rebuild and both cyinders were right around 130 and my bike is complety stock

[Hank]

It's got me a little stumped because it starts first or second kick. I bought it a month ago and seemed to run fine but the guy said the top end had never been done. Pulls strong on the bottom end but seems to be lacking in the mid and top. I guess I will take the head off and see what it looks like inside.

[Building my First]

Are you using a good tester with the proper tip? Did you hold the throttle wide open and kick it several times?

[Hank]

I used the correct tips, just not sure how good the tester is? I did not hold the throttle wide open. Would that make a significant difference in the psi reading?

[Hank]

Ok, got a new compression gauge and it reads 115 psi on both cylinders. It usually starts the first or second kick so I believe the compression should be ok. Thinking of purcahsing a cool head with 19cc domes to get a little more compression. What kind of octane should I run with that head? I have some VP C12 that I run on my KTM but not sure if that is too much octane (108). Will that help improve my throttle response in the mid to upper range? Thanks...