I have been grappling with this problem for over a month now. I have already replaced the fuel lines thrice and this time around I pressure tested the lines for leaks before I put them in and on the tank. So pressurisation problems can be ruled out.

No compression means no compression. I found that at that critical temperature, the prop simply turns over by finger. You dont even get the push-back you are talking about. Let it cool a couple of seconds and the compression returns. Loss of compressio seems to be happening a bit randomly. Remember I have already got black oil in the exhaust two or three times within 3 weeks and I have already checked to ensure that everything is as tight as feasible. When I take-off, it runs for a couple of circuits and then deadsticks. This is with the needle set rich and with the stock muffler and with a 13x6S2 prop doing only level flying. Both times this weekend I could tell that the engine was about to deadstick because I could hear the rpm wavering in the air. And everytime I heard the waver, the engine cut-off in less than a few seconds.

Think I have eliminated most of the variables. Please suggest if I have missed something, I will try that out as well. Point is, I want to replace the engine while I still have the airplane intact.

Still, if I do put in a 75 or a 91, I will use a lower pitch prop- 14x4 or so. I dont think a 15" will fit. And I am planning to use a Dubro anti-vibe beam mount I already have to prevent too much vibration stress on the airframe. In any case, I never use full rpm on my airplanes even at take-off as it is simply unnecessary- if you have sufficient take-off run it will lift itself at 60% throttle.

Ameyam