I have a .72 Magnum Four Stroke Engine mounted sideways/down on a piper cub. The engine worked fine up until the last time i tried to fly it. After setting the mixture on the ground, i would lift the nose high to check for stall at full throttle. The engine will run fora few seconds then flame out suddenly. I have remixed many times and it always does thesame thing.I reset the valves to spec and it has not helped atall. Does anyone have any suggestions on what i should try next? I run 15% nitro with 16% Castor oil.

Will