# Fuel Pump Question



## Lawddog (Jan 2, 2020)

Hey Fellas, 
Quick Question about the fuel pump on my 66 GTO (Motor is a 421 out of a Bonneville). There is a small fitting with a pin hole in it, is that the return fitting? Pic attached. 

Thanks, 
V/r Jason


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## PontiacJim (Dec 29, 2012)

Yes. It should be larger than a pin hole, so never have seen this - maybe the Chinese quality control missed this one. Maybe the housing serves a dual purpose in that some Pontiac's do not have a return line while most AC cars will. So they make 1 base so it will be applicable for the non-return line applications and then simply drill that fitting out for applications needing the return line. Only way to find out is when you fire it up. If it pushes out gas the minute you fire up the engine, just plug it off with a piece of rubber hose, bolt, and 2 hose clamps.
That's my cheapo but practical fix.


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## Lemans guy (Oct 14, 2014)

Right the return orifices are small, and the line is usually 1/4 inch. One the fuel filter the return line opening is very small about .060......that is the diameter of the whole I use on my homemade return line after the fuel log.

Return lines are not vapor lines, they return liquid fuel but the purpose is to keep fuel moving in small amounts so that the fuel does not dead head in the line between the pump and the tank, if it does the vacumn pulled will lower the pressure in the line and lower pressure allows fuel to boil at a lower temperature and turn to vapor.....vapor won’t pump...so vapor lock.

just look up the pump specs and see if it says it has a return line.....if that is the only line that is it. Hard to tell the size of the orifice, but a return orifice is small or the pump would lose too much pressure. Pumps also have a small vent hole, sometimes on top....

try PJ’stest use a bucket.....it it squirts has like PJ said that is it...lots of 67 and later pumps had a return fitting.


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