I have a 1956 Thunderbird with a 312 and manual transmission. I have a problem with the mechanical fuel pump in that when climbing a steep hill the car runs out of gas unless I turn on the auxiliary electric fuel pump. To try and fix the problem I rebuilt an original AC mechanical fuel pump with a kit from Then And Now. Unfortunately that did not fix the problem. So I pressure tested and flow tested the rebuilt pump. It passed the pressure test but on the flow test it only produced a 1/2 pint of fuel in 30 seconds rather than the 1 pint called for in the shop manual.
To make sure that the problem was not in the input line from the tank, I bypassed the mechanical pump and ran the input line directly to the carb so that I could run the car with just the electric pump. I then ran an independent input line from a free standing gas can to the mechanical pump and ran an output line from the mechanical pump to a container. I started the car but the mechanical pump still only produced 1/2 pint in 30 seconds.
Does anyone have any suggestions as to why the mechanical pump is not producing an adequate flow of fuel? Did I miss something in the rebuild?
Thanks.
Jim Yergin

when you rebuilt the fuel pump did you replace the check valves also or just the diaphragm? I was having the same problem but after rebuilding the fuel pump I have never had the problem since.

Is this a problem that has developed, or was it always a problem with this pump?

If there are no restrictions and the check valves are seating properly, the only other reason I can think of for insufficient volume would be insufficient pump stroke. Maybe the pump eccentric is worn out?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Thanks for the responses.
This has been a problem from the start with this pump. It was also a problem with the previous pump which is why I installed this rebuilt pump.
Jim Yergin

Can you measure the eccentric for wear. 

I think I would have to pull the front cover of the engine to get to it. I would rather not have to do that if possible, but good suggestion. My engine only has 60,000 original miles on it and when I refreshed it 10,000 miles ago I did not notice any wear on that part.
Jim Yergin

Is your pump an off-shore aftermarket pump? There have many complaints regarding off-shore (China) fuel pumps. For that reason, Casco is paying $50 for rebuildable pumps made in USA and Mexico.

Sounds like your tank pickup sock is plugged up a bit.   Hard for a vacuum pump to keep up, but the electric pump overpowers the clog.  Joe-JDC

JDC

Thanks for the responses.
The pump is an original AC pump that I rebuilt.
I don't think it can be a problem in the tank because it had the same low flow problem when drawing gas from an independent gas can.
Jim Yergin

Jim, did you operated the pump by hand before installing it. I do that with every pump I’ve ever put in. A bad one sounds different than a good one. Also can you look in the hole with a mirror and a light to see the eccentric? 

56 Vic, B'Ville 200 MPH Club Member, So Cal.