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F134 idles but backfires when driven normal and bogs out

Discussion in 'Early CJ5 and CJ6 Tech' started by seabass1858, Aug 27, 2013.

  1. Aug 27, 2013
    seabass1858

    seabass1858 Member

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    I have an f134 that idles beautifully but as soon as you get on the gas is sputters and back fires along with going down the road. I was able to drive at higher speed even in of but it's constantly back firing slightly. The carb is freshly rebuilt to include throttle shaft bushings. What could possibly be going wrong what other settings could be off.
     
  2. Aug 27, 2013
    PeteL

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

    Hills of NH
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    Timing? Point gap?
     
  3. Aug 28, 2013
    seabass1858

    seabass1858 Member

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    Timing is good and I got the pertronix upgrade
     
    Last edited: Aug 28, 2013
  4. Aug 28, 2013
    PeteL

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

    Hills of NH
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    "The carb is freshly rebuilt"

    Vacuum leak on the intake? Check the carb base gasket (and maybe check if the mounting flange ears are bent from over-torquing).
     
  5. Aug 28, 2013
    Fr8 dog

    Fr8 dog Member

    Cincinnati
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    Did it run okay at speed before the carb rebuild? If it did, I'd suspect that it would be something wrong with the carb rebuild. The fact that it idles well leads me to believe that it's not a vacuum leak and the idle circuit is metering fuel okay, but when you open the throttle, engaging the main metering circuit, the fuel mixture is not proper. My guess would be that, while operating in the main metering circuit, that there is not enough fuel being metered, thereby making your mixture too lean.

    If it ran this way before the carb rebuild, that opens the door to a potential ignition problem. Good luck

    Brad
     
  6. Aug 28, 2013
    uncamonkey

    uncamonkey Member

    Greeley CO
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    If it were me, just rule to out the valves, i'd do a compression test.
    Then go from there.
    Always good to know those numbers.
     
  7. Aug 28, 2013
    PeteL

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

    Hills of NH
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    Vacuum leaks often idle okay but show up when under load.
     
  8. Aug 29, 2013
    Fr8 dog

    Fr8 dog Member

    Cincinnati
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    Yeah, I can agree with this. The mixture would be leaner but could be compensated for by opening up the idle mixture screws, then when the throttle plates open up, engaging the main metering circuit, the vacuum leak causes the lean mixture leading to the original complaint. One way or the other, too much air or not enough fuel, I'd bet your fuel mixture is too lean above the idle circuit.

    Brad
     
  9. Aug 29, 2013
    bobo

    bobo Sponsor

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    Do you have full 12 volts to your petronics?
     
  10. Aug 29, 2013
    seabass1858

    seabass1858 Member

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    I adjusted the metering rod and it seems better, I can now get it into od. Compression as follows 74,74,75,74 cold, 121, 123, 121, 121 warm. there is a full 12v going to the pertronix. It still seems a bit rich though and it sounds like its backfiring in the muffler. I was 8 years old when it really ran last and I had the carter rebuilt by a reputable antique auto restoration shop that works on Hudson's and packards. They also put new throttle shaft bushings.
     
  11. Aug 29, 2013
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    Go back and check the timing again. And if you have one of the timing lights that will do the advance readings also, have some one open the throttle up to say 2500 and see if the timing marks change. If they don't, then the mechanical advance is sticking and causing the miss and backfire stuff.
     
  12. Aug 29, 2013
    kamel

    kamel Senior Curmudgeon

    Erlanger, Kentucky
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    I would agree that it could be in the distributor....

    When accelerating the weights in the distributor advance the timing to accomodate the acceleration. That would cause it to idle OK, but not operatie properly under load. You can lubricate the weight assembly without taking the distributor out with some spray lube that has a tube nozzle that you can stick inside the unit, although in a worst case scenario you may have to remove the points/condenser, and plate that they mount on. That plate is held in by the same screws that hold the clips on.

    I would try using oil on it first without disassembling anything. Only as a last resort would I take those componenets off. It isn't hard to do, but it opens opportunities for dropping and / or losing parts.
     
  13. Aug 29, 2013
    F Bill

    F Bill Member

    Abilene, TX area
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    Cold compression readings are a bit on the low side. Is your valve adjustment on spec?
     
  14. Aug 31, 2013
    seabass1858

    seabass1858 Member

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    no i did a fresh rering kit, no rebuild just new bearings and rings. the internals were pretty good them selves
     
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