Strange fuel issue

LogansLT

New Member
Feb 28, 2022
5
Good morning! First post but have used the site for some time. Great info on here. Need help with a strange issue. My 16 yo picked up an all original 74 LT. It has the 350 w/quadrajet. This may be a little long but necessary to explain the issue we are fighting. What appears to be happening is that the fuel return from the pump to the tank is getting backed up and somehow is causing the fuel pump to build excessive pressure. This in turn is blowing past the needle and seat in the carb and flooding the engine. New tank, new pump and all lines are free and clear. If we blow the fuel out of the return line, hook everything back up, car runs great for a little bit then starts flooding again. Last night we directed our attention to the charcoal can. Thinking that the vacuum supplied to the tank from the carb, through the can is what may be needed to help "pull" the fuel on the return side into the tank. We are getting good vacuum at the carb side of the can, but nothing on the tank side of the can. Anyone run into this before? My Chevelle doesn't use the factory return since I have replaced the stock pump with an Edelbrock pump with no return and I have no issues. We even took the carb off my car and put on his to see if he had a weak needle and seat, but had the same issue with my carb on his car. Sorry for the long post. Appreciate any help.
 

LogansLT

New Member
Feb 28, 2022
5
Do you get the same symptoms running it without the return line?
Last night we connected a hose directly off the return port on the fuel pump and ran it straight to a pan. Car started running fine within a minute. Seems like both pumps (original and replacement) do not have enough pressure on the return side to push the fuel back into the tank. That is where the EVAP vacuum theory came into play. Thanks for the response.
 

LogansLT

New Member
Feb 28, 2022
5
During the flooding scenario, I did slowly remove the gas cap and heard no built up pressure noises.
 




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