Going to agree with Rodney here. Tank location is number one. You need to lower the tank. Many people invert engines and leave the tank in its original position which is now far above the carb line which makes it a royal nightmare to tune the engine.

I have several inverted engines where as i changed all this and I have no problems at all. I dremel out the bulkhead to lower the tank but strengthen around the sides to compensate with epoxy and such