I didn’t get a chance to work on it last night, was getting my son ready for his first Boy Scout Jamboree. I usually tune my engines by setting the high speed needle to max rpm then turning rich about 300 rpm, then turn barrel to idle position as low as it will idle and let set for a minute or two then increase throttle fast and listen for an abundance of fuel ( engine stumbles) or lack of fuel (engine just dies quickly), then I adjust the idle mixture screw the appropriate way then readjust the high speed needle again then back to idle and keep going this way until it runs smooth and good.

I am starting to wonder if it would be the needle at all because the engine was running great and normal for 3 flights and then right in the middle of the 4th flight it started this behavior, I have never had a needle just turn itself out of tune all at once. I am thinking there might be a blockage because when the barrel is quickly fully opened from idle, the engine doesn’t stumble or anything, it just slowly in a matter of 5 seconds increases rpm to normal wide open rpms just like if you slowly opened the barrel, then at full rpms, if you pinch the fuel intake line the engine increased in rpm, and then dies just like normal.

It is almost like there is a restriction in the inlet and when the barrel is opened, the pressure builds in the tank from the exhaust and starts to push more fuel into the carb and that creates more pressure and pushes more fuel and so on until the engine cannot build any more because the air through the carb has reached the full flow rate.

Sorry for the long winded reply, but I will try the idle mixure screw tonight.