One of my Saito 91s started in reverse for a few moments then stopped - this in itself is nothing new but this one had no compression afterwards. Eventually I stripped it down to find the problem and found a bit of the PTFE tape I'd used for the exhaust thread had been sucked back in and was clogging the inlet valve open. Simple to fix but a bit worrying at the time.

Perhaps something similar going on with this engine?

Richard