RTK thanks for your input it all helps, the tuning could be the problem, or that is what I am hoping. You may have to go in to more detail on that one for me. As far, as air over the carb causing a vacuum or whatever. Most of the problem is more evident when I put the aircraft in a hover; you would think there would be no more airflow over the engine than there would be on the ground because it is stationary in the air.