Well, my 1st question is what altitude are you at? I live above 9,000' and after a new top end, I only get 90 PSI cold and 100 PSI hot. You do have to compensate for the altitude you're testing compression at. Machine runs fine at 90.Hi. I need some help. I have a 2002 Polaris trail RMK 550. The manual says spec compression is 120 psi. Its fan cooled. I did a rebuild, new crank, new pistons, new rings. I gapped the rings and the pistons were the right size. The cylinders were honed. I reassembled used oil and broke it in but I am only getting 90 psi compression. I have used 3 different testers and tried them on another older sled that read 110 psi. The sled seems to run ok, start ok, except when it is warm and I stop for a few minutes and just let the sled idle and then when I push the throttle to go it bogs down and dies. I have to let it sit a few minutes and then pull it several times before it will start. Is this because I have added oil to the fuel for the break in or is it something else? Also should I have a good shop machine down the head cover or should I have them machine down the cylinder housing? Is it better to do the head cover or the cylinder housing? Am I stupid to do either one? Thanks for any help.