Trouble w/ fuel pump 1955.1

[Gundu7475]

Hey all. I have a mechanical question. I have a 55.1 4400 series dump. I just rebuilt carb and replaced fuel pump. Truck started but fuel pump stopped pumping. I removed it and set it on vise and hooked up a small fuel tank and pumped it. all good. put it back on and nothing…not pumping. It was primed as well. Im at a loss… is there an actuator in there that may not be spinning? What could be causing this?? Thanks so much in advance.

[dwcsr]

if the vacuum on the suction side is to great they will not pump. make sure the line is not clogged or the rubber line is not collapsed

[Gundu7475]

Ok the lines are solid and I blew through them with no apparent obstructions. However when i removed the pump there was some old rust in the new pump. I cleaned it before putting it back on. Then I hooked up a small gas tank right next to the pump so it wouldn't have to run through the rusted lines again. There are no kinks in line either. I didn't know about too much suction and it won't pump though. What would cause too much suction? Thanks for your help.

[dwcsr]

Let me rephrase that. if the line is clogged or the rubber collapses and it creates a high vacuum the diaphragm hangs and won't pump until the vacuum is released. Like wise if the pressure on the output side rises to high it will hang and not pump until the pressure lowers and the float drops, all this is normal. have you tested the pressure at the carb? or tested the suction with a gage?

[Gundu7475]

I have not tested the carb or the pump with a gauge. What should the gauge read? Thanks so Much for spending some time on this.

[dwcsr]

checking the pump pressure at the car it should be about 5 psi. on the inlet side it should draw a good vacuum of about 18 min. You may have a stuck float. If the float hits the side of the carb housing it can stick closed or open.

There is a possibility that the pump is no longer any good. I have seen that when a new pump is installed and the tank has crud in it it embeds in the rubber valve seats and pressure doesn't build. Put a filter in the line before the pump even if this one test good.