Fuel Pump Functional Tests

Fuel Pump Test:

NOTE: Prior to performing fuel pump tests inspect all hoses and lines, for kinks and bends that may cause restrictions. The following tests will check fuel pump pressure, volume, and vacuum.
1. Remove the air cleaner assembly and disconnect the fuel inlet fitting at the carburetor.
2. Disconnect the fuel return hose at the fuel filter and plug the nipple on the filter.
3. Connect a pressure gauge, restrictor clamp, and hose between the fuel filter and carburetor. Position the hose and restrictor so fuel can be discharged into a graduated container.
4. START and operate the engine at curb idle speed, and discharge fuel into the graduated container by momentarily opening the hose restrictor. Close the restrictor and allow the pressure to stabilize. The pump should develop 28-34 kPa (4-5 psi). If the fuel pump does not develop the listed pressure and the fuel filter is in good condition, the pump is defective and must be replaced.
5. START and operate the engine at curb idle speed. Open the hose restrictor and allow fuel to discharge into the graduated container for 30 seconds, then shut off the restrictor. The container should have at least 470 ml (16 oz) of fuel captured. If the pump volume is lower than the volume listed, repeat the test using an alternate fuel source. If the volume is still below the specification the pump must be replaced. If the pump volume increases, look for a fuel line or tank restriction.
6. STOP the engine, reconnect the fuel lines at the carburetor and fuel filter, START the engine and check for leaks. Reinstall the air cleaner.
DIRECT CONNECTION VACUUM TEST
NOTE: The direct connection test is used to determine the fuel pumps ability to create a vacuum.
1. Disconnect the inlet fuel line from the fuel pump. Wrap a suitable shop towel around the fitting to catch any fuel spill.
2. Connect a vacuum gauge to the fuel pump inlet fitting. START the engine and allow it to run at curb idle. The vacuum gauge will not begin to show vacuum until the fuel in the float bowl is consumed, and the pump begins to operate at maximum capacity. The vacuum reading should increase to approximately 34 kPa (10 in-Hg) If the vacuum does not increase to the specified level the fuel pump is defective and must be replaced.
3. STOP the engine, remove the vacuum gauge, reconnect the fuel fitting and test for leaks.
INDIRECT CONNECTION VACUUM TEST
NOTE: The indirect connection test is used to check for obstructions in the fuel tube or in the in tank fuel filter.
1. Disconnect the fuel inlet tube at the fuel pump, and connect a "T" fitting between the inlet tube and fuel pump. Connect a vacuum gauge to the other position on the fitting.
2. START and operate the engine at curb idle speed until the fuel in the float bowl has been consumed and the fuel pump begins to operate at maximum capacity. Increase the engine speed to 1500 rpm, and hold at that level for 30 seconds. The vacuum should not exceed 10 kPa (3 in-Hg). If the vacuum exceeds the specified level, check for an obstruction in the fuel supply line or in the in tank fuel filter.
3. STOP the engine, remove the vacuum gauge, reconnect the fuel fittings and test for leaks.