2fast4u hit it on the head. Many engines have problems with inverted mounting. Having the engine well broken in before mounting it this way will help. Mine is on it's side. The carb just seems weird. In order to adjust the low end you have to open the throttle some, otherwise it seems to bottom out. The engine was never run before and I'm the 3rd owner. It is mounted in a Global Tecate Bipe and the previous owners thought it would be too much for them. They should have given it a chance, it flies quite well, even when the motor quits!