Fuel Pump
1977 Johnson/Evinrude 55HP Outboard motors
The fuel pump is of the diaphragm-displacement type, and is operated by changes in crankcase pressure.
Alternate suction and pressure in the crankcase are transmitted to the pump diaphragm.
Vacuum created on the upward stroke of the piston causes the diaphragm to displace and draw in fuel through the inlet valve.
On the following downward stroke of the piston, crankcase pressure flexes the diaphragm in the opposite direction. The inlet valve is then seated, preventing the return of fuel to the tank, while the discharge valve is opened, allowing fuel to pass to the carburetor.
Fuel is drawn through a fine filter screen before entering the pump to remove impurities. See Figure 3-2.
Updated on: Sunday, December 6, 2020