I had a similar problem but it was with a Zama carb. It would run for a few minutes on the gas/glow fuel and then it had real problems in the air. I would then remove the fuel from the carb before leaving the field. When I tried it again several days later the same thing happened. The carb had the original black diaphragm. After that I replaced the diaphragm with a replacement, it was still black but definitely a different material. It worked fine for about 5 or 6 flights and then something happened and it would not work at all. Anyway, after that I replaced the carb with a Walbro having a blue diaphragm and changed to EI. It has worked fine ever since then on gas/oil mix. About 25 flights with no carb problem. It might be that the diaphragm is effected by the gas/glow fuel especially when fuel is flowing at max rate. I suggest changing to a fiberglass diaphragm.