97 Polaris Sportsman 500 Compression

I recenly bought a 1997 Polaris Sportsman 500 not running. I try to make it turn with the electric starter with a full charge batterie, but went it turn over the motor stop turning after 2 stroke. I remove the sparkplug and I put my compression tester and first stroke 30 pounds and second stroke 60 pound and then it seem that the compress air wont release. I need to release the air to make it turn again. Do you think that I have a valve or valves stuck?:th_smiliepullhair: