I was given an older entry level (I think) Sears walk-behind mower with a very common Briggs & Stratton 4.5 hp motor. The kind with the carb on top the gas tank as an integral part of the gas tank. It has the primer-bulb carb. I am a LawnBoy man, not Briggs, so I am not too familiar with these 4 cycle carbs. Between the carb body and the fuel tank is a thin rubber membrane AND a gasket. I have reason to believe this mower was worked on before and possibly not reassembled correctly, as I found the mower blade installed upside down. What I need to know is this: Does the rubber membrane go directly against the underside of the carb body, then the gasket between that and the tank? Or is it gasket, membrane, tank?