[leegreen]

I'd never realized that mechanical pumps used the spring to power the pump cycle and the cam arm was the return stroke. But is does make sense, the spring gives some pressure regulation, if it was the other way there would need to be a pressure relief.

So now the boost pressure bleed to pump makes sense, the spring needs the extra pressure to get the fuel pressure high enough for the carb when it is under boost. Now the electric pump makes sense too, it turns on from the manifold switch to put enough pressure on the intake side of the mechanical diaphragm to overcome he boost pressure and fill the diaphragm chamber. Without the electric pump the diaphragm would flex away from the boost pressure and the pump volume would fall off.

If you are replumbing anyway, bypassing the whole works in favor of a modern electric pump, filter, non blocking regulator and return line to tank is probably a more reliable approach. less historically interesting but your truck, your call.