Have a 30 year old 250cc Polaris Trail Boss 2 cycle and had the cylinder bored and a new Wiseco piston and rings added. First test I couldn't get higher than 75 PSI on a brand new compression tester. So I assumed that the rings moved off their pins when I installed the cylinder and took everything apart, double checked the clearances, ring gap, etc. Installed brand new gaskets and re-torqued to spec and getting 75PSI and sometimes if I pull hard almost to 100PSI. I'm holding full throttle when I am testing.

Would the crank bearings or seals impact the compression? I've got the exhaust and air box off - but would assume that helps improve compression? I've also got the nipple where the old goes into the engine open if that could impact anything...looking for a plug for that...

 

Does it run?
If so, run it a while to seat the rings. Comp will prolly come up.