Dave, This is my first YS 4 stroke... experienced with several YS Heli motors... Here is the problem

20/20 fuel, OS F plug, 13x6 APC prop. Mounted on a Funtana. I am getting 10,600 rpm and 2000 ppm idle.

Starts ok, warm it up and take off. The funtana does not require full power so most of the flying is around 1/3 to 1/2 throttle. After prolonged flying at lower power setting (1 to 2 min) the engine starts to sputter like it is rich. Playing the throttle when it first starts will clear it. Sometimes this results in a dead stick.

After the run the tank is bulging with pressure. Fuel filter going into carb is clean.

Main needle is 1 1/4 and Idle screw is flush with the barrel.

The APC Prop might sound like it is too much but it is a narrow blade version that is revving to 10,600.

I figure it is a cross over problem... ie idle to pressure delivery. I guess I do not understand the idle screw...is is an air-bleed or fuel quantity mixture screw? The transition seems good on the ground.

Any help appreciated.

TIA
Bert