Hi, I suggest you test the pump out of the car, attach a hose to the inlet, put it in some fuel or water and hand crank it.
You should be able to blow through the pump from the inlet side, or suck from the outlet. You should not be able to do it the other way, if you can it's the check valves failing.
If it works then either the arm is too short, due to a spacer between the pump and the block preventing a full stroke or the carb float valve is locked shut.
Good luck.