also take off the line that runs to the carb take the tip off that connects to the gas tank but leave the other end connected to the carburetor and blow through the hose listen real close you might have an air leak check the base of the carburetor,the backplate,where the exhaust connects to the motor,and if all these are sealed and not leaking then unscrew the hsn all the way out and check the o ring if it has any cracks or anything replace it