A mechanical pump can be checked any one of four ways: Remove the air cleaner, look into the throat of the carburetor and pump the throttle linkage. You should see fuel squirt into the carburetor if the pump is working.

Pressure Valve Method

1. Open your hood and loosen the nut from your negative battery cable.
2. Locate the cap on the fuel supply manifold.
3. Use the valve to drain the fuel into a sealable container, such as a plastic jug or a drain pan.
4. Wait for the excess fuel to drain and then press the pressure relief button.

Relieving Pressure with the Fuel Pressure Regulator

1. Disconnect the negative battery cable using a wrench.
2. Locate the fuel pressure regulator on the fuel rail.
3. With your hand, remove the vacuum hose from the top of the fuel pressure regulator.
4. Connect a hand-operated vacuum pump to the top of the pressure regulator.

You don’t need to manually prime a mechanical fuel pump the way you do a carb. A fuel pump works on a vacuum; at idle speed, a well-functioning fuel pump should draw enough of a vacuum to prime itself.

The standard mechanical fuel pump found in classic cars is very reliable. Nevertheless, nothing automotive lasts forever. If your car has an external fuel pump, you’ll probably run into situations that will require you to test and possibly replace this component.

Mechanical fuel pump As the shaft turns, a cam passes under a pivoted lever and forces it up at one end. The other end of the lever, which is linked loosely to a rubber diaphragm forming the floor of a chamber in the pump, goes down and pulls the diaphragm with it.