Fuel Pressure: Testing and Inspection

SYSTEM TEST:

1. Using a Tee fitting and fuel hose, connect a low pressure fuel pressure gauge in-line between the fuel pump outlet and the carburetor inlet.
2. Start the engine and observe the gauge readings.

Fuel Pressure: 2.5 - 3.5 PSI

3. If fuel pressure is zero, ensure that the fuel tank has fuel. Also check fuel filter for blockage or restriction.
4. Raise engine rpm to 3,000 rpm and check gauge reading. If a drop in fuel pressure occurs, remove the fuel pump for component testing.

Removing Fuel Pump:

5. If no problems are found, remove the fuel pressure gauge from the engine.
6. Reconnect all fuel hoses.
7. Start engine and check for fuel leaks.

COMPONENT TESTS:

1. With the fuel pump removed from the engine, operate the pump lever by hand and check for excessive arm play tension.
2. Block off the outlet and return pipes with your fingers and check that there is an increase in lever arm play. Ensure that the lever arm moves freely indicating that air is trapped in the pump.

Checking Fuel Pump Inlet Valve:

3. Block off the inlet pipe with your finger and check that the pump arm is now locked (cannot be depressed easily). DO NOT force the arm to depress.

Checking Fuel Pump Outlet Valve:

4. Check the pump diaphragm by blocking off all three of the pipes with your fingers and attempting to depress the pump arm. It should lock as in step 3.

Testing Fuel Pump Diaphragm:

5. If any deficiencies are found, replace the fuel pump.
6. Block off the vent holes under the pump casting with your fingers. Check that the pump arm locks.

Inspecting Fuel Pump Oil Seal:

7. If the arm does not lock, the oil seal is bad and the fuel pump should be replaced.
8. Reinstall the fuel pump on the engine cylinder head.