Other than dirty gas line screens, three things should be checked on the fuel pump if trouble is experienced. First check for loose valve plugs (Fig.5). If the valve plugs are loose the pump will fail to deliver the required amount of gasoline to the carburetor. Tighten tile valve plugs securely. If necessary, replace the valve plug gasket.
If the valve plugs are tight and in good condition, next check for either a broken actuating spring or a leaky diaphragm. The diaphragm may leak either from a puncture through the diaphragm material or a leak at the edge where the diaphragm is secured to the pump body. Tighten the cover screws evenly and securely. Shellac should be applied to the edge of the diaphragm either under the diaphragm on the surface, which comes in contact with the fuel pump body or on the outside of the body at the point where the diaphragm protrudes. Sometimes there appears to be a leak at the diaphragm whereas the leak actually exists at the pipefitting and the gasoline has run down the pump body to the diaphragm flange appearing to originate there.
Just under the diaphragm in the side of the pump body will be found a small hole through the pump body wall. If gasoline leaks out through this hole, the diaphragm should be checked for a leak through the diaphragm material. If the diaphragm is found to be leaky, replace with a new diaphragm. The pump diaphragm is actuated by a coil spring. The pump cam forces the diaphragm down and the spring as soon as the cam releases forces the diaphragm up. In service it sometimes happens that this actuating spring breaks, thus weakening the spring action against the diaphragm. If this condition exists, trouble may be experienced at high speed from lack of gasoline. To correct, replace the diaphragm actuating spring.
Information Donated by Carol Rush