Take out one head shim in order to raise the compression. Next turn the high speed needle all the way in, then turn it out 3 1/2 turns. Also, cheack the fuel line for clogs, then cheak the gas tank for cracks by submerging it in water, holding the fuel line shut in one hand and blowing through the pressure line. If bubbles come from anywhere (the lid might pop up due to air presure)then you know that you have an air leak and that would make tuning the engine a real pain in the arse. After that cheak the backplate and under the carb for air leaks by tightening the screws on the backplate and loosening the pinch bolt on the carb(or whatever holds the thing in place), putting pressure on the carb body, and then tightening it back up. By doing this you ensure that there are no air leaks IN the engine. If all else fails, then simply rebuild it.