3/8 10mm PETROL PUMP

Function and technical context

The manual fuel priming bulb with 3/8" (10 mm) connection is part of the fuel supply system between the tank and the engine on MerCruiser outboard and propulsion boats. By repeatedly compressing its body, it pushes petrol along the fuel hose until the circuit is purged of air and the engine can start normally. Without effective priming, the carburetor or injection system does not receive the minimum necessary supply, which makes starting impossible or causes startup failures. The tightness of the internal valves of the bulb is what guarantees that the pressure generated does not dissipate back to the tank, ensuring a constant unidirectional flow.

When to replace this part?

The most common symptoms of a primer bulb in poor condition are loss of firmness when pressed (it remains soft even after several presses), the appearance of visible cracks in the rubber body, fuel leaks at the connection joints or the inability to maintain pressure once the circuit has been primed. Hardening or discoloration of the elastomer—common after several seasons of exposure to the sun and hydrocarbons—also indicates internal degradation of the valves. It is recommended to inspect the condition of the bulb at each seasonal inspection and replace it if there is any sign of deterioration, since a failure in navigation can leave the boat without propulsion in the middle of the sea.

Compatible Mercury MerCruiser Engines