Reply To: 57 Johnson 7 1/2 Starts but won’t run

[billw]

Obviously, you’re not a rookie, so you have the tank gas cap screwed down snug. My first guess is the rubber check valves behind the intake manifold, that allow tank pressure to build. I have seen some that deteriorate and don’t seal right. If you don’t build tank pressure, no gas gets sent back to the carb and the engine dies. The tank primer just sends enough fuel to fill up the carb again. It doesn’t pressurize the whole tank.

Long live American manufacturing!