Check your tank height in relation to the SPRAYBAR in the carb and make sure the clunk is free moving in the tank. The tank/spraybar height is most likely the reason the engine dies out on you while inverted. When engines are inverted (or the plane is flying inverted) the tank height becomes critical to proper running.

As for your transition problem,

1. Make sure the fuel is fresh.

2. Try an OS #8 plug. If that doesn't help, try an OS #A3 plug. You will most likely need to adjust your low end/high end after the plug change.

Fresh fuel AND the proper heat range plug can improve 98% of transition problems.

Hope this helps.