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Coincidence With A Full Gas Tank??

Discussion in 'Intermediate CJ-5/6/7/8' started by Holty, Nov 9, 2020.

  1. Nov 9, 2020
    Holty

    Holty New Member

    Pa
    Joined:
    Aug 6, 2020
    Messages:
    23
    1977 cj5 304 2bl 4-speed. I filled the gas tank and after a few miles, it started to run rough, backfire, won't idle. After throttling for a couple minutes it cleared out and on my way. I will happen again but not always. This is the second time it has happened after filling it full.
    Out of the sending unit there are two nipples, one feed, one vent. Both attached ok. I do not have a charcoal canister up by the firewall, but the hose is there. New fuel filter. On the fuel tank, drivers side, there are two nipples. Someone has looped the two together. What are the nipples for?
    I do think it is fuel related but I checked cap, rotor, wires. All good.
    Can filling the tank to the top be effecting this.
     
  2. Nov 9, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
    Joined:
    Aug 3, 2003
    Messages:
    9,754
    Yes, IMHO, if you don't have functional venting system.

    A (non)-venting situation would show up faster when the tank is full. A partly empty tank would need more time to develop a high vacuum in the vapor space.

    See if the problem occurs if the gas cap is left loose.
     
  3. Nov 9, 2020
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
    Joined:
    Jul 18, 2013
    Messages:
    5,593
    guessing if the fuel tank nipples are looped together - instead of going to a charcoal canister - that the tank is not venting properly. I used a later cj tank in my early cj5, and I looped the nipples on the tank (no charcoal canister on the early cj5), but then I had to modify the fuel cap to vent.
     
  4. Nov 9, 2020
    zila

    zila I throw poop

    Rock Springs,...
    Joined:
    Oct 6, 2003
    Messages:
    1,201
    My 75 was wonky when I first got it. Dying and coughing etc etc.. Finally I dropped the fuel tank and.... There was some real nasty stuff in there.. Dumped it , blew all the lines out, replaced and filled up. Problem solved
     
  5. Nov 9, 2020
    Jeff Bromberger

    Jeff Bromberger Quarantined in the Garage

    Dallas Metroplex...
    Joined:
    Jun 28, 2019
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    202
    In my Jeep DJ5 (postal Jeep), we have those two nipples on the fuel tank, too. They are attached to a fuel vapor condenser, mounted inside the left rear fender. The two inputs are on the bottom and come from the tank and are supposed to take vapor and either drip it back down to the tank, or (if there's the right situations), draw it from the bottom output port to the charcoal can in the engine compartment. This, of course, is vacuum bled into the engine, so that captured vapors are burned and not let loose into the world...

    Now, in practice, how effective is this? I don't wanna offer any guesses...
     
  6. Nov 9, 2020
    zila

    zila I throw poop

    Rock Springs,...
    Joined:
    Oct 6, 2003
    Messages:
    1,201
    I ditched mine.. Then installed EFI later..
     
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