I have been looking though all the old threads on this problem and thought I would start a new post so that I could let you now what I have found out without digging up an old 2 page thread. The problem with these engines were determined to be that on the old engines, with the solid cast metal rear needle valve was that the engine would run lean at mid range. I discovered this and so for the most economical way to fix it, I cut the needle vavle off the back plate very carefully and attached it with two threaded screws to a plastic piece that was attached with the engine mount bolt to the firewall of my big stick 60. WELL, this did not fix the problem. I have the exact same problem as before cutting the valve off the back plate. The engine continues to mis at mid range. I flew an entire tank through the engine at mostly full throttle (it flew fine, head was cool enought to touch), landed and refueled, took off and did a few touch and goes without raising the throttle above half and all of a sudden when I went to full throttle, the engine would not pick up rpms and died on landing. It was hotter than a two dollar pistol. I hope no damage was done in the short 4 minutes that I was flying it at half thottle. I assume from this that when running at full throttle (and it also idles well) it was fine but it was lean at mid range and finally got too hot to run. My next course of action will be to put a supertiger carb I have laying around on it and see what happens. I am thinking that instead of a heat issue, that this is really a vibration issue and that the engine vibration travels though the engine mount and into the needle valve mounted to it.

I am using 15% magnum fuel with 18% oil blend, a 14x6 MA S-1 prop. Peak rpm about 11,500 richened up to 11,000. The engine has new bearings.