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'78 Gas tank breather??

Discussion in 'The Garage' started by southernspeed, Apr 20, 2005.

  1. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    I've got a 3/8 feed hose and a 1/4" return hose on my '78, but how does the gas tank breath?? Is it through the gas cap? I'm just putting in EFI and am concerned I'm not going to get enough venting on the tank. Any ideas? :confused:
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I've had some real issues getting my tank to "breathe" correctly as well. Slightly different situation, but...

    I've got the '87-91 sending unit, which of course has the EVAP fitting. Problem is, truck was diesel, no EVAP. So I plugged that line (temp until I figure something out better) and ran what is *supposed* to be a vented gas cap. Here's a pic:

    [​IMG]

    As you can see, there are two valves on this cap, later ones have one valve, and only "vent" at a much higher tank pressure. In my case without the vented cap, pressure got high enough to tell when you removed the tank, but this cap has also started to do the same.

    I know you aren't in the states, but crossreferencing truck caps that wouldn't have had EVAP with ones that did at places like napaonline.com netted me the same part numbers, which can't be correct.

    Personally I like the EVAP setup as stock. Safe, efficient, protected while water crossing, etc. Just don't feel like retrofitting it to my truck. If I can find another "vented" cap, I will try it and see, if not, I will have to vent my tank through the sending unit and try to keep from having problems that come with that, such as foreign objects getting in the line, water, condensation in the tank, etc.
     
  3. TorkDSR

    TorkDSR 1/2 ton status

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    interesting, my 79 had 3 hoses, and one went to the charcoal can....
     
  4. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Mine's definately only got two and my old style gas cap has 'warning, remove slowly' on it, making me think that isn't vented but it must be as it's never been a problem with the carb. I guess it should run ok with the TBI but as I was redoing some of the fuel lines I wanted to get it sorted out all at once. Maybe I could 'T' into the big breather that goes from the sender to the filler hose and run to a canister?
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    You probably could t like that, but then again, GM ran a valve in the EVAP line, just more potential issues.

    Not entirely sure which purposes it served, but on a carbed app the valve was probably solely temp controlled.

    I ran EVAP on my car with no valve straight to the carb quite a few years back, (and I never had a problem) but now I think that isn't that great of an idea...fuel vapor, backfire, line straight back to fuel tank with no "check" valve. :(
     
  6. captaininsano

    captaininsano 1/2 ton status

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    Interesting my 78 has a little vent hose on top of the tank with one of those plastic vent thingys on it. Kinda worried about my new filler cap myself since it is pretty dang hickified. Going to go with a plastic "cap" I think, not sure I like the metal on metal current config. Also I wonder what the smog guy is gonna think next year, technically it holds pressure. :D Cali sucks! Hoping to have a trailer and 1-ton tow rig by next year anyways...

    [​IMG]

    [​IMG]

    [​IMG]

    http://silverlegend.biz/wheelin/page_02.htm
     
  7. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Hmmmm...looks like there's a plumber in town! :grin:
    Haven't seen a plastic breather thing on mine, I'll have to have a closer look.
     
  8. captaininsano

    captaininsano 1/2 ton status

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    Yup kinda cheesy but I am sick of my gas cap getting ripped off every trip or fuel spilling out of the stock cap when the truck is on its side. This way it is protected, sealed, and easily fillable. I never knew Osh sold gas fillers...
     

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