I am helping someone with a 27 chevy truck that is having a fueling issue.
Background info: it has the original 4 cylinder engine that utilizes a stewart warner vacuum tank (the taller skinny one) to get fuel to the carb. After being in storage for several years it was time to get it running again. Gas tank was previously sealed with a gas tank sealer that decided to become a big ball of gunk in the bottom of the tank. When last run, the vacuum tank and carb were completely drained and on inspection were completely clean and free of any gunk. due to the condition of the gas tank, it was replaced with a boat tank with a plastic tank with vented gas cap. When i got there the engine started right up and ran like a top several times, and ran for a about 5 minutes each time. The last time it ran for a little longer. We went to lunch and came back and fuel was seeping out of the vent on the top of the tank. We drained the vacuum tank checked over the lines, removed the check valve at the gas tank, and restarted the truck, drove it for about 10 minutes and parked it. fuel line was leaking a little bit just downstream of the gas tank so we fixed it, and restarted it. now the truck will run for about a minute or so and die. It sets for about a minute and will restart, run for about a minute and then start again, run for a minute and die again.
Process of elimination, the carb was removed, checked over and reinstalled. no change. Fuel filter is about 2/3rds full when running. Removed gas cap from fuel tank to make sure it is venting, still no change. Next day while i am not there, they put a rebuilt carb on it, no change. Removed fuel tank and directly gravity fed the carb, truck ran until they shut it off. Pulled top off the vacuum tank, inspected it, said nothing appeared to be blocked or broken and ran the truck with just the fuel in the vacuum tank and it ran like a top for a long time, until they shut it off. Put the top back on the vacuum tank, started the truck, it again runs for about a minute and dies. Fuel filter has gas in it, carb bowl has gas in it, but it won't stay running. While it is running there is a steady stream of air bubbles entering the fuel filter, but the filter remains over half full, with the outlet side fully covered with gas.
All of this seems to point at something wrong with the vacuum tank, but not sure what would be causing this. It seems as though something is keeping fuel from flowing- like there is vacuum leak somewhere that is keeping the fuel from flowing while running, but i am not sure where to start tracking this down.
We are committed to keeping the vacuum tank and not putting in an electric fuel pump.
Any suggestions from folks who know more about this setup?
Thanks in advance!