I get this low compression once in a while from a four stroke? There are no ports in the sleeve but I have been told that the ring rotates and if it is in the right/wrong spot you will have low compression. It comes back after running. The two strokes have a pin or slot to keep the ring from rotating so they shouldn't have the problem. As mentioned, if the engine runs this well and I can get up to the working RPM range with that prop then there must be enough compression while the engine is running. I felt no gain in compression weather the engine was hot or cold. One of the first things I did was shoot some oil in the combustion chamber to see if that made any difference, nope! I do think I will end up getting a compression gauge for glow engines, I have them for my gassers but I never use them very often. Still, A new toy!! I'm sure this engine is just fine and will get better with age and use. It was pulling my cinder block around on the concrete with 50 pounds of lead on the block so I know it has that tug factor!!