Electric Fuel Pumps and Carbs
Steve,
I suspect that what you're seeing in scenario 2 is pump related. By that I mean, the typical universal pump is electric solenoid; pulsing on and off constantly by means of a small magnetic cylinder which are audible clicks. Normal by design. The guage will flutter.
There is another type- roller vane by the same manufacturers. It is larger as it has a motor. I suspect it to be constant as is the mechanical OEM pump is for most certain.
All carb'd pumps regardless of design should have a check valve and funtioning so that it stops reverse flow to the tank, easy to check, and faulty if not. I suspect that some hard starting problems are related to this check valve and siphoning back to the tank. ( There are marine check valves available for the same pupose which I may try to stop this from happening; but I just put on a new mechanical pump very recently as it was less than spec, but working.)
If you're carb float/ valves and pump check valves are functioning, you should have some residual pressure for a short while. You might have to pinch closed the fuel line at the pump, shut down, loosen a clamp at one carb and then repeat for the other. The repair manual has a procedure; you just have to improvise a bit.
One other item of note; the QC on these pumps can be spotty. Just last week, a fellow member here went through 3 pumps. ( 1 failed, replacement was bad, third worked.) The parts person didn't even blink on the return.
Hope this helps,
Jerry
61Porsche
