Our friend and longtime OMC Tech, Joe Reeves, has posted thousands of answers to technical questions about Johnson and Evinrude motors on our Boat Repair Forum. He started contributing to the forum in 2001 and is still at it! He has helped countless visitors solve their engine problems. Here are his tips on Fuel Pump Diaphragm Tests.
Fuel Pump Diaphragm Test
Two Hose Type Only
by Joe Reeves
Note: This section pertains only to the regular Two Hose type fuel pumps.
Leave the hoses attached to the fuel pump. Remove only the two screws that attach the fuel pump to the powerhead. Re-insert those two screws and install a nut to each of them so that the fuel pump is securely clamped together. With the fuel line attached to the engine, pump the primer bulb while observing the pressure/vacuum operating hole on the back side of the fuel pump. Should any fuel leak out that hole, the diaphragm is faulty.
If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.
Fuel Pump Diaphragm Test
Three Hose Type Only
by Joe Reeves
Note: This section pertains only to the regular Three Hose type fuel pumps.
Remove only the pressure/vacuum hose that leads from the fuel pump to the crankcase. Leave the other hoses attached. With the fuel line attached to the engine, pump the primer bulb while observing the pump pressure/vacuum fitting that you just removed the hose from. Should any fuel leak out that fitting, the diaphragm is faulty.
NOTE: If the carburetor is obviously flooding, clamp the hose shut that leads to the carburetor.
If the diaphragm is faulty, the fuel pump will require rebuilding or replacing. Note that repair kits are not available for all fuel pumps, in which case replacing the pump would be necessary.
Editor’s note: Please also refer to your specific engine diagrams and a Service / Repair Manual for your model for additional information.
