We repair inboard boats. Usually if the pump acts up, as above, during hot weather or hot soak periods, it means a new fuel pump is in order. You can get by for a while keeping the motor box vented or pouring cold water on the pump but typically it would need replacing. The pumps that are mounted in the tank, we found fair worse than the ones mounted in the engine compartment. When the fuel in the tank is 1/4 to half and you make a sharp turns, the fuel sloshes to one side and runs the pump dry for a second or 2. Over time it also ruins the pump.