I have a compression tester for glow engines. I was wondering how to accurately test my OS 61. Should I just slowly turn the prop, or flip it or run it up with the starter? Also, what is an acceptable number for the old ringed OS-61 FSR?

Thank you

Bob

Flip the engine by hand very briskly to get a good compression reading. Several flips will do the job. As far as numbers go, we don't have any. O.S. doesn't provide any. If your engine is running well, then check its compression and see what number you get. Then a check from time-to-time will let you know if it's falling off. How the engine's running is a very good tell-tale to determine if you need to check compression.