Unless you are totally dead set against working some more material out of the way, I, personally, would open up the intake in front of the engine cylinder some more.. Maybe with a sanding drum on a Dremel to open that hole to the point where the cowling starts to roll back toward the tail.. maybe take the sides out a little more just to be sure the whole jug is getting fresh air. That is where I would start, it would take the least amount of time. Unless, like I said, you are dead set against opening any more holes on it..