just what I was thinking soil!! He means an airleak anywhere on, in or around the engine.. Check the carb fitment, check the back plate where the pull start passes thru, check the front bearing for excessive fuel leaking out(Thus air leaking in), check the head gasket, check the exhaust gasket for tears, check the air line going to the engine for air bubbles, check the fuel tank for holding pressure and finally check the exhaust nipple to see if its plugged. But a smal airleak can be big troubles!!

Good Call Soilwork!!