Your pump element has two motions if working properly... vertical travel in response to fuel cam lobe, and rotation in response to governor rack movements. The plunger can become stuck and stop working without it being that apparent from an external inspection. Check carefully to insure that the element plunger has free rotation and full vertical travel. You can always pull the pump and manually check that the pump has free motion. Other than this, there is no mystery to that fuel pump. If it has an air-free supply of fuel, then it must pass the fuel out the top when it is operated. If you really cannot seem to resolve the difficulty, it is possible to swap the pump out altogether... these are readily available and not terribly expensive. Any buddies nearby? Sometimes another set of eyes/hands can spot the problem even though you have been methodical in your own approach to it.
dieselgman