Agreed but where? As the bulb draws fuel in from the boat side, it could be an anti-siphon valve in the tank or something coming from the boat. If you look carefully at the port side belly pan you will see two hard plastic semi clear lines coming into the motor. One is the oil line the other is the fuel line. Carefully start the motor on cooling muffs and monitor the fuel line for air bubbles. That will give you a good starting point.