Not on the ground but in the air the engine pops, it almost sounds like timing. It doesn't seem to effect the performance of the engine, it just doesn't sound as smooth in the air as on the ground. I thought it was just my SPE 26, but a another guy has the same engine and his has the same popping sound. We were just wondering if maybe the muffler hole was too big and the engine didn't have enough back pressure????

If you have the Chinese plug in it I would start by changing that.

I have one in my H9 T-craft and it runs smooth and quiet, I would have to agree with SOARRICH about the sparkplug although I am using the China plug and so far so good. Make sure the top end is not to lean because this could also cause a popping sound ( Backfire through carb ) Good luck !!

Thanks, it seems to do it more at mid range then full throttle. One of the Gasser guys at our club said Gasser's do that. Also what plug would you recommend?

Do you have the slipstream blowing over the carb? If you do you may want to put a velocity stack on it and a air defector in front of the carb. The fact that it's the mid range makes me think you L needle is too rich. I set my engines up by running them at ~3500 rpm and leaning the L needle, as you lean it the engine will speed up, lower the rpm back to ~3500 with the throttle. I do that until the engine sags or dies, then I back the L needle out about 1/8th of a turn. You then need to idle the engine down to ~2000 rpm and pop the throttle open if it dies open the L needle 1/16th of a turn at a time until it speeds up quickly every time. Now readjust you H needle for max rpm.

NGK BPMR6F, is the plug to use....

Thanks for the help