Fuel system Vented or Non-Vented EFI conversion

Discussion in 'The Garage' started by 73k5blazer, Dec 31, 2006.

  1. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

    Dec 28, 2001
    Likes Received:
    The Rustbelt
    Ok, so I'm putting in EFI (port FI, 45lbs fuel pump required, not TBI which requires much lower pressure) in my 1973 K5, I have a 50gal Hickey Gas tank, which has already been Renu'ed. Being that it's already been epoxy coated, it's somewhat difficult to modify at this point.

    So, I need to add a fuel return line. Problem is, my tank has a 3/8 pickup out the front, a 3/8" vent out the side, the main filler and 5/8" filler vent and that's it. So if I use the vent outlet on the tank as the return inlet, how can I vent the tank, or does it even need vented?

    Does a fuel system need to be vented? I think so, but I'm not an expert here. From the factory it has a non-vented gas cap. But I belive that top vent tube was just plugged, but some hack before me could have done that. It did have a charcoal canister from the factory, but it was not hooked up when I bought the truck in '92. Whenever I removed the gas cap after a long trip, it would make a giant sucking sound, probably as air filled the vacuum created inside the tank.
    Would it be acceptable to tee in a vent line into the filler vent? Or possibly plumb the fuel return line into the filler vent? Where should I vent it to? Does it have to go to a charcoal canister? Can I just put a little breather on the vent line, providing I can find a method to vent the tank?

    BTW, thanks to advice from Paulmoon, who was burning up pumps with his EFI conversion, I decided to use this type of setup with a surge tank (swirl pot):
    The surge tank has it's own vent, but that's already on the backside of a the low pressure pump, so it's not vented the tank.

    Thanks for any advice.
  2. ntsqd

    ntsqd 1/2 ton status

    Nov 28, 2002
    Likes Received:
    So. CA
    The tank needs to be vented somewhere. Venting to a charcoal cannister in good shape & correctly plumbed means that you won't occasionally be smelling raw fuel and you won't be leaking fuel out of the gas cap when off camber. Not to mention that it will also act as a filter of the vent air to keep junk out of the fuel.

    One fairly common EFI return set-up on a non-EFI tank that I've seen is to drill & tap the filler neck somewhere for the return hose fitting.

    An option on the accumulator or swirlpot is to use BCB's Filter-Accumulator set-up.

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