The B series engine uses three different piston style fuel transfer pumps. All three deliver different flow volumes.
Piston style fuel transfer pump, Part No. 3918076, is offered as an option on B series engines equipped with
distributor type fuel injection pumps.
NOTE: Part No. 3918076 and 3918000 are identical in appearance. The pumping spring free length can be measured
to identify the fuel transfer pump.
Fuel transfer pump 3918076 spring free length 53.5 mm [2 7/64 in].
Piston style fuel transfer pump, Part No. 3918000, comes standard on the 300 HP marine B series engine.
NOTE: Part No. 3918076 and 3918000 are identical in appearance. The pumping spring free length can be measured
to identify the fuel transfer pump.
Fuel transfer pump 3918000 spring free length 58 mm [29/32 in].
Piston style fuel transfer pump, Part No. 3921550 comes standard on the 91 B series engines equipped with the
Bosch P7100 in-line fuel injection pumps.
Piston style fuel transfer pump, Part No. 3925709, comes standard on the 94 B series engines equipped with the
Bosch P7100 in-line fuel injection pumps.
The piston style fuel transfer pump is mechanically driven by a plunger running against a special lobe on the cam
shaft. The fuel transfer pump contains a pumping piston and check valves to control the flow of fuel, and bleed
back during engine shutdown.
Normal pressure drop across the fuel filter is 35 kPa [5psi], maximum.
The pressure drop will increase as the fuel filter removes contamination from the fuel. Therefore, a worn fuel trans
fer pump will have reduced capacity to force fuel through a dirty fuel filter. This can cause low engine power.
NOTE: Frequent fuel filter replacement to get full power from the engine can indicate a worn transfer pump.
The output of the piston style fuel transfer pump can be checked two ways.
Test 1: Measure the output pressure using an in-line pressure gauge.
Test 2: Measure the flow volume.
Test 1: Output Pressure Test (Piston Style)
Operate the engine and measure the output pressure of the fuel transfer pump using an in-line pressure gauge.
Test 2; Flow Volume Test (Piston Style)
Caution: To prevent the engine from starting , disconnect the fuel shutdown wiring . Residual fuel in the fuel
injection pump may cause the engine to start.
Caution: Do not crank the starter for more than 30 seconds at a time, Doing so may result In starter damage.
Also, high voltage during cranking may damage the shutdown solenoid.
Disconnect the fuel shutdown solenoid wire and measure the engine cranking speed with a hand held tachometer.
Caution: Leave the shutdow n solenoid disconnected for the following check.
Disconnect the output pressure line from the transfer pump and run it into a container.
Crank the engine for 30 seconds and measure the fuel transfer pump flow volume.
Use the chart in the illustration to find the correct flow volume specification for P/N 3918076 fuel transfer pump.
• Draw a straight vertical line above the measured cranking RPM.
• Draw a straight horizontal line from the measured flow volume to the engine cranking RPM vertical line to find the
intersection point.
• Any intersection point above the required flow line indicates an acceptable flow.
• Any intersection point below the required flow line indicates unacceptable flow and a defective pump or too much line restriction.
Use the chart in the illustration to find the correct flow volume specification for P/N 3918000 fuel transfer pump, used on the 300 HP B series marine engine.
• Draw a straight vertical line above the measured cranking RPM.
• Draw a straight horizontal line from the measured flow volume to the engine cranking RPM vertical line to find the
intersection point.
• Any intersection point above the required flow line indicates an acceptable flow.
• Any intersection point below the required flow line indicates unacceptable flow and a defective pump or too much line restriction.
Use the chart in the illustration to find the correct flow volume specification for P/N 3917334 fuel transfer pump, used with the Bosch P7100 in-line injection pump.
• Draw a straight vertical line above the measured cranking RPM.
• Draw a straight horizontal line from the measured flow volume to the engine cranking RPM vertical line to find the
intersection point.
• Any intersection point above the required flow line indicates an acceptable flow.
• Any intersection point below the required flow line indicates unacceptable flow and a defective pump or too much line restriction.
If the flow volume measured falls below the line in the respective chart above, check inlet restriction before disassembling and cleaning the fuel transfer pump.
Inlet restriction must not exceed 100 mm Hg [4 in Hg].
If the fuel is aerated or the volume is low, isolate the fuel transfer pump by connecting the fuel transfer pump inlet
to a temporary supply and perform the same check as above.
If the fuel transfer pump delivers the required volume of fuel from a temporary supply, check for restrictions or
suction leaks in the fuel circuit to the fuel transfer pump:
1. Supply line
2. Pre-filter
3. Supply line
4. Supply tank
5. Tank vent
Look for a plugged supply tank vent first.
Replace or clean the pre-filter.
In cold weather look for gelled fuel blocking the pre-filter.
Look for kinks that can restrict the fuel supply lines.
Remove and blow out the fuel supply lines.
