1995 Puma Typhoon 2.5cc

Ian I used these for practice combat. Very crude engines, ( Fox .35's of combat engines). But, they deliver moderate power. Nothing like a modern F2D engine. With the correct prop, I use the Russian glass props, they can turn up into the 27-28K range. I can get it to turn more but it's just not useable power. I made a Nelson head for mine. ABC construction which is somewhat like dinosaur in combat due to weight. I picked up two for $30 at a swap meet. It has a nasty attitude initially until broken in. It cost more in plugs than the trouble it was worth to do so.  This was very frustrating to break in. I had to add a lot of head shims and a lot of bench running which shouldn't be necessary for a combat engine but it was worth it. It now readily starts and is reliable. Unfortunately, it's real loud. I can only fly this engine at our sister field alongside of a airport due to the noise. I only run this on 10A% nitro. The rear exhaust is a pain in the rear. It can and will melt foamie wings even though the exhaust is directed in a Y. When you go to adjust the needle, the exhaust burns the hell out of your thumb. My findings were the same as yours internally. I chamfered many parts and cleaned up a lot inside.  Ken