ORIGINAL: av8tor1977

When an engine runs good on the ground and then goes rich in flight, it is usually caused by the carburetor regulator sensing ram air from flying, which makes the carburetor go richer. What you need to do is solder a 1/8'' tube into the regulator cover on the carb, and then run a hose from there into the fuselage where it can sense static, and not ram, air. The regulator is the cover with four screws and an open hole in it. When you make the existing hole larger and solder a tube into it, make sure that you grind everything flush and smooth on the diaphragm side of the cover so that the diaphragm does not get damaged by any rough or high spots on the cover.

Also note that when running an engine with the cylinder oriented upwards, if the engine is running a bit rich in general, fuel can accumulate in the crankcase, especially if you are flying around at mid or low throttle settings. Then when you invert the plane, the accumulated fuel drops into the airflow inside the engine making it suddenly go very rich.

AV8TOR