Your poll and the subsequent responses don't seem to tackle probably the most fundamental problem with 4-strokes not running very well inverted.

Look at the relationship between your engine and the fuel tank. You need to make sure you fuel level is slightly higher than the centerline of the carburetor. Some inverted engine/airplane configurations forget this important step and you end up with a fuel tank much higher than the carburetor. This causes the carburetor to fill up with fuel when it is not running.

I had a significant problem with my U-Can-Do 3D because of this (inverted Saito FA-100). My solution, and many others, was to add a Cline Regulator to my fuel system. This keeps the fuel from flowing to and flooding the carburetor between flights and allows me to reposition my fuel tank to the CG. Others have modified the airplane to position the fuel tank lower in the fuselage.

IMHO, the OS #F plug is the way to go in most 4-strokes, regardless of manufacturer.