How To Test Fuel Pump

Engines with carburetors

  • Make sure there is gas in the tank
  • Look for any bends, or kinks in the fuel line. Older rubber fuel line can be damaged by ethanol. Replace with fuel injection line.
  • Disconnect the fuel line at the carburetor.
  • Disconnect the distributor coil wire so the engine doesn’t start while cranking.
  • Use a suitable container at the end of the fuel line and crank the engine a few revolutions. If little or no fuel flows from the line, either the pump isn’t operating, or the fuel line is plugged. Disconnect the fuel line at the pump inlet and at the fuel tank. Blow air through the line to make sure it is clear.
  • If fuel flows from the line at the carburetor in good volume, check fuel pump pressure to make sure it is within specifications.
  • To test the pump pressure, connect a fuel pressure gauge to the pump line at the carburetor, then run engine 500-1000 RPM. If pressure is not within specifications or varies to any extent at different speeds, repair or replace the pump.
  • For the pump that puts out too much pressure, think about installed a regulator between the pump and the carburetor.
  • Check your motors manual to be sure of the pressure specification, otherwise 4.5 would be a good target.
  • Pump vacuum test.
    • Disconnect pump inlet line and connect a vacuum gauge to the pump inlet fitting. Disconnect the pump outlet fuel line from either the carburetor, or the pump (necessary to allow the pump to operate at full capacity). Use a length of hos and container to receive discharged gasoline. The pump should produce 10″ of vacuum at idle RPM.
Updated on 04/13/2022

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