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

The idle screw is an air bleed. Clockwise is richer. It should have no effect on the midrange. At 1/4 throttle you are already above the suction to pressure point. I never idle them that slow as I like to be into the regulator at idle. 2300 or so will do it.
My guess is that the regulator is set to rich, but I could be wrong. Try running the reg in about 1/2 turn and see if it improves.

Thanks Dave I will give that a try...