Fuel Pump Caution on Marine Inboard Engine

AERA members have reported confusion when replacing mechanical fuel pumps on marine inboard engines. Many marine inboard engines were fitted with fuel pumps which, when the diaphragm ruptures, allow fuel to spill into the bilge. This creates a very dangerous situation that can lead to an explosion, if the operator of the boat fails to activate the blower system to clear the bilge of fumes prior to starting the engine or auxiliary generator.

Later fuel pumps are equipped with a hose barb to route the fuel through a tube to a similar fitting in the air horn of the carburetor. This permits excess fuel from a failed fuel pump to spill into the intake manifold. While this will cause the engine to run rough or choke out, it does prevent fuel from spilling into the bilge.

Earlier systems can be updated by replacing the fuel pump with the later style, barb equipped, fuel pump. Complete the installation by installing a hose barb in the carburetor and attach a piece of flexible tubing to the carburetor at one end and to the fuel pump at the other end.

Many fuel pumps are used on more than one type of engine which requires different locations for inlet, outlet and separator fittings (where applicable) in relation to the rocker arm. The location of these fittings can vary even when used on the same engine. Always use the old pump as a guide. The locations of these fittings are expressed in terms of clock positions with the rocker arm located at 12 o`clock as viewed from the top of the pump.

It is important to note that while proper use of the blower system will clear the bilge of excess fumes, it will not stop them from continuing to accumulate from gasoline in the bilge which has not been pumped overboard by the bilge pump. Most often the blower system is turned off after the engine is started and the boat is under way. It is far safer to leave the blower system on while there is someone aboard and an engine is running. Installation of a sniffer is advisable, as it will sound an alert when fumes have accumulated and the blower system should be turned on.

The AERA Technical Committee