RE: G-26 ZENOAH, FLAMES OUT
1. Sounds like over heating. Try flying without the cowl. Make sure to compensate for the cowl weight on CG. Then if no issues you need to open up the cowl bottom, especially as mufflers get really pretty hot and air can circulate in the cowl. Temp gun could check cylinder head temp below 180-185 F.
2. Also check you carb standoff block for any cracks . Sound a lot like mY friends zenoah. Exhibited same perfect on the ground then poor in the air. Had a crack in the block. I never would have caught it as it was cracked on the underneith side.
Good luck.