Do you have a static line hooked to the carb and run into the fuslage? You don't want to block the static hole. It is there for a reason. The carb uses static pressure to meter the fuel it flows. If air blows into the hole it will create pressure causing the engine to go rich in the air. If air blows over the hole it can cause it to go lean. By installing a pressure tap in the hole, grinding it smooth on the inside, and run a line from it into the fuslage, the problem may be solved. It is a common problem with gas engines. The carbs are not really made to have air blowing all around them.