Ford F100 Fuel System

There are a couple things here. In the first place if you can pump fuel with the pump off the engine and pumped by hand doesn't mean that it will pump on the engine. See the stroke on the engine is very short, it only moves like 1/4 inch. So you could have a bad pump even though you are pumping by hand. The gas cap, will have no effect on this model. Yes the pick-up tube has a filter on the bottom of it, and it could be stopped up. You can remove this unit up through the top of the tank, got to wiggle it and turn it sideways, and if you can find a used one( New ones scarce and expensive) by going to used parts place, and look for 1967 - 1972, they are all alike. Lots a luck in fixing this great ole truck.

How hard was it to pump it by hand?Iwould be suprised if a mechanical fuel pump could be easily pumped by hand as the spring pressure required to hold the arm against the eccentric is considerable If its a cleveland or windsor you cannot pump by hand.I own a 1980 running a cleveland and found that if you put an electric pump as close to the fuel tank as possible and have a good original mechanical pump fuel delivery is no longer a problem.I had to do this as soon as i went to a 600 holley as the original pump was not able to supply sufficient flow.the electric pump doesnt have to be an expensive hi volume type,it only has to help to get fuel to the mechanicl pump