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Thanks in advance for your help on this question....I have to replace the fuel pump on my '65 327/300...it is a 15 year-old "generic" pump (without the AC markings). It does NOT have a vent tube on the top...just in and out lines. BUT.....in looking at the replacement pump sold by Volunteer Vette Products (local to me) their description says the new generic unit, while "clocked" correctly for lines in and out, DOES have a vent tube on the top. Of course, they sell a "correct" pump with the AC logo and without the vent tube, but, surprise, it costs about 5 times what the generic model costs. I am no longer doing NCRS meets so I don't care about the correct markings. My question is, is there a problem or an issue with installing a unit with the vent tube? I don't want to run a line back to the gas tank, nor do I want to use a charcoal canister. If installed, should this tube be either capped OR left uncapped? Either way, would this cause vapor lock or running issues such as in hot weather that wouldn't occur on a unit that didn't have the vent tube? Thanks again for your advice and input. (Similar pump pic below is from Summit's website).
Last edited by gilbybarr; Jun 18, 2026 at 10:47 PM.
The only time I've seen mechanical fuel pumps with vents (as opposed to a return line) is in marine applications. They usually are hosed to a connection at the top of the carburetor (above the choke). The idea was to provide a path for fuel leaks caused by a failed diaphragm --- a fancy weep hole. If that's the case then you can simply leave it uncapped or if you feel frisky run a hose off of it to somewhere that fuel can safely drip. If it's a return line then you should cap it off. Those were intended to relieve pressure after shutdown as an aid to preventing vapor lock.
P.S. The 2nd photo was not displaying but now that I see it that is definitely a vent not a return so it's ok to leave it open or run a hose away from anything hot.
Last edited by acstephenson; Jun 18, 2026 at 10:50 PM.
If memory serves, the Carter street/strip pumps I have run have a vent hole. For a marine app they drill the hole over size so they can press in the vent tube. Functionally the same I believe. When I run a marine pump in an auto application, I like to put a short hose on the barb directing any future leak towards the ground.
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Replacing Fuel pump with one that has a VENT TUBE
