Can it really be that sensitive to fuel tank position? I noticed that the tank center line is indeed about 1/2 inch lower than the needle valve.
Mike,
My experience is that 1/2” is OK on a 40 with an eight-ounce tank.
If the engine were mine I would take it out of the airplane and bench run it with a different tank. The purpose for bench running would be to check slightly different tank positions and maybe discover anything else that might be strange. For cautionary reasons I would take the high speed needle out make sure the fuel entrance is absolutely clean. In addition I would run a 10 X 6 prop until the problem is solved.
The problem can be found but it seems like it requires an infinite amount of patience sometimes.
Taking off rich will eventually bring about the disaster we all like to avoid.
Bill