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Vacuum To Fuel Tank Makes For Hard Starting.

Discussion in 'Early CJ5 and CJ6 Tech' started by Buildflycrash, Nov 19, 2019.

  1. Nov 19, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

    Gulf Breeze FL...
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    1966 CJ5, 225 V6, relocated 1979 rear tank, 3 line pump with return to tank.

    Crank, Crank, Crank if Jeep has been sitting for more than a day. When at gas stations it can hear/feel the air getting sucked in when I loosen the cap.

    Yes I deleted the vent when I put it together. I was thinking of just drilling a tiny hole in the cap. Any better (easy) solutions?

    [​IMG]
     
  2. Nov 19, 2019
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    Whoa! That happened accidentally to me once, and the vacuum collapsed the tank.

    Plus the tank was behind the seat in my J-2000, and it scared the poop out of me when it suddenly caved in.
     
  3. Nov 19, 2019
    Twin2

    Twin2 not him 2020 Sponsor 2019 Sponsor

    Virginia Beach, VA
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    without a carbon canister . you need a vented cap
     
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  4. Nov 19, 2019
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    +1.

    You could run a line from the vapor recovery ports to a high point in the rear corner, open through a fuel filter.
     
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  5. Nov 19, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

    Gulf Breeze FL...
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    I’ve looked for a vented cap. I’ll look again or do you know where to get one? Wouldn’t drilling a tiny hole be the same as a vented cap?
     
  6. Nov 19, 2019
    Twin2

    Twin2 not him 2020 Sponsor 2019 Sponsor

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    I would do as tim suggested . hose with gas filter on end
     
  7. Nov 19, 2019
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    I’ll see if I can reach the vent area. I just might be lucky.
     
  8. Nov 19, 2019
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    No really. They have a kind of one-way valve in them.
     
  9. Nov 19, 2019
    Beach66Bum

    Beach66Bum 1966 Tuxedo Park Mark IV 2020 Sponsor 2019 Sponsor

    Big Island on...
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    I bought a vented gas cap (chrome) off eBay years ago (4 years)
     
  10. Nov 19, 2019
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
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    I'm a hose with fuel filter person on two riggs in the top rear fender where the fuel fill is on my custom setups. Tried to get a cheap carbon filter for dirt bikes, but it never came back in stock.
     
  11. Nov 20, 2019
    scott milliner

    scott milliner Master Fabricator

    Seattle Wa.
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    Vented caps only let air in. What you really need is a Carbon Canister. I mounted mine in the rear wheel well.
     
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  12. Nov 23, 2019
    Wayngro

    Wayngro New Member

    Central WA. state
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    Ok, I've my tank our right now. I want to eliminate all that venting crap as well.
    So, I'm thinking I can cap one of the vent elbows and run fuel line up and away from the tank to a high point for venting with a fuel filter or whatever on it? Is that what youse guys is sayin?
     
  13. Nov 23, 2019
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    What year tank? There are a few different designs. According to your profile, you have a '74 which should be similar to the tank pictured above (good to put that info in your signature file, then it's in every post). I would tee the vapor recovery lines together and run them up into the corner. Jeep puts a liquid check valve (later called an "anti-rollover" valve) in the vent line so liquid can't come out of the vent. If you have the original vapor recovery plumbing, I would urge you to keep it since it does not affect performance and vents your tank properly, as well as preventing fuel stink and recovering fuel evaporation to be burned later... all while keeping the air clean. No real downside IMO - removing it is kinda wrong-headed.
     
  14. Nov 23, 2019
    Wayngro

    Wayngro New Member

    Central WA. state
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    1974. Has the same two vent tubes coming out of the top of the tank like the OP's. There's some "junk" in the driver's side rear fender corner, way up high, with a couple of hard plastic tubes running down to the two tubes on the tank and some wires. Then it looks like at least one of the hard plastic tubes runs up front, I'm guessing to a vacuum source? Anyway, I already pulled what I believe to be the charcoal canister from the engine bay and might as well remove this stuff too.
     
  15. Nov 23, 2019
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    A '74 has a liquid check valve in the rear corner that the vent lines run to. From this, a single nylon vapor line runs forward to the vapor recovery canister. A single purge line goes to the factory air cleaner. This system is simple - easy to understand, zero maintenance, and several benefits. No sensible reason to get rid of it. Trying to help you, but it's your privilege to reject my help.

    Described in chapter 4A here https://oljeep.com/gw/74_tsm/4A-EmissionControl.pdf page 17, free to read and download.
     
  16. Nov 23, 2019
    Wayngro

    Wayngro New Member

    Central WA. state
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    Hey, thanks for the help with that. Seein that I've most of the items left to complete that set-up, I might just run that.
     

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