Just replaced the orings on my Noss Head. Background: Did pistons and rings last year this time and compression test with my 19cc domes at sealevel read 183psi just as it should be with minimal riding since then. Had some trouble with sparkplug leaking oily residue out top of head so i decided to replace head orings and plugs as precaution.
Just took head off and installed new oring kit, replaced head, did a compression test. All of the sudden my comp test showed 210 psi each cylinder. Did test 3 times each cylinder, WOT and not, regardless read the same.
Im going to try the comp tester on another bike to ensure tester is not bad but just curious if anybody knows why this might have happened or had this happen to them before.