I put a 472 Cadillac in my Mercury and I am having problems getting fuel to the carb. I am use too the fuel pump having only one inlet and these pumps have two, one is 3/8" and the other is 5/16". I believe one is an overflow and the other is the supply so I put both into a gas can to see if I cand get the motor to start but I am not getting fuel to the carb. Is there anybody that can explain this fuel system to me so that I might understand what I am doing wrong. I am attaching a drawing showing how I have it hooked up.
The smaller line is a return line, it needs to go back to the fuel tank. The large, non-threaded fitting is the inlet. The threaded fitting is the outlet. Is the pump new? or was it on an old engine?
The smaller one is the return line. But, it should work the way you have it set up. Try putting your finger over each port while you are cranking, you should be able to determine which are suction and which are discharge. ~Alden
it is the old pump but worked great when it was pulled out I will check for suction if nothing I will just replace. i thought maybe the return line needs to be be in the gas can but not in the gas its self to produce suction
No, the return line just needs to be in the gas can to keep gas from spraying all over the place. Look for bug deposits in the fitting holes. Sometimes they get in there and plug things up. Also used pumps don't like sitting around, they dry out and don't work.
sounds like I just need to replace it. the motor has sat for a few years so I will just put in a new pump. thanks for the help
With today's gas, I'd run a return line if it's not too much trouble. Helps with the vapor lock/flooding issues.
Yeah, run the return line...my '55 Caddy, with Caddy 500", started vapor-locking...so I put in a new mechanical pump and redid the fuel lines, made sure the return line, off the pump, went all the way back to the tank...haven't had a problem with vapor-locking since then...even running cheap gas... R-
good to know I will go to the parts store and see what I can get. my tank has a return on it so running a return should not be a problem
Does your fuel pump have a 1 1/16 inch nut on the outlet side? There is a fuel filter in there if it does. Remove the filter and make sure it does NOT have the check in it. On the Cadillac the fuel flows in the opposite direction through the fuel filter and if the check valve is installed there will be no fuel flow. You should also look in the mounting hole with a light if replacing the pump and crank the engine and make sure the BOLT ON fuel pump eccentric is turning. The eccentric is located by a metal tab that is bent over into a hole in the end of the camshaft. I have seen this tab shear off.
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