tuffy

Hoping someone can help me with compression here. I just acquired a YL1 that had been sitting for over 20 years. Rebuilt carbs, replaced battery, replaced petcock, sealed tank, replaced plugs and changed all fluids. Started right up after 2-3 kicks and after adjusting idle and air screws it seems to idle ok. I am able to put it gear but it just has no pick-up when trying to take off. If I pull hard on the throttle while in 1st gear it seems to not bog so much. I tested compression of both sides with plugs out, throttle open and engine warm on a cheap compression tester. Got 60 compression of both sides. Next I put some oil into the spark plug openings and tested and now I got 120 on left and 90 on right. This seems off since on the first test they were both 60. What is the optimal PSi? Neither the Clymer or service manual seem to state this explicitly (that I've found). Is it possible that this tester is inaccurate or am I doing something incorrectly? This is my first time testing compression on a bike. hoping I don't have to replace rings but am prepared to do so if need be. Thanks in advance.