What prop and what was your RPM. You should be in the range 6400 to 7100. The Fuji 50 should have been enough power to loop at just over ½ throttle. What is your total weight? Is the engine under any warranty? If yes, send it in for service. Hope you get it working, the Eagle is a great flying plane. If this is your first gasser than I would try to solve the problems with the Fuji, you may have other issues that are messing the engine up. Heat build-up is just one. If you change engines you may have the same problem. I would find a guy in you area to check it out. The Fuji is a good engine for your first gasser.