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Carb Issue On 1979 Cj-5

Discussion in 'Intermediate CJ-5/6/7/8' started by bcurtman, Aug 4, 2017.

  1. Aug 4, 2017
    bcurtman

    bcurtman Member

    Rosebud, MO
    Joined:
    Jan 8, 2014
    Messages:
    283
    Jeep has 36,xxx original miles. It is equipped with a remanufactured Carter BBD carburetor, same as it came from the factory with.

    Here's the dilemma.

    The jeep, once started runs and drives as it should. Starting it is the problem. After sitting for a day, you have to crank it long enough to pump gas back up to the carb, as there is none present to start the jeep.

    Here is what I have observed.

    After it set for a couple of days I pulled the air cleaner off and while looking down into the carb, moved the throttle to wide open. It gave a pump of gas from the accelerator pump as it should. But that's it. One pump. Subsequent pumps produces no gas into the throat. If you crank it it will hit and die.

    Then, you must crank it long enough to pump gas back to the carb, pump it, and it will start. I'm talking maybe 10 seconds of cranking.

    Is there a check ball or one way valve (yeah I know the needle and seat) that is not allowing the fuel to remain in the bowl, allowing it to leak down, or do I have a fuel pump problem? I have a new fuel pump setting here, but don't want to throw parts at it that it may not need. Is the needle perhaps not seating? I havent taken the carb apart, but I thought the needle and seat were typically not in the bottom of the bowl. Your input is appreciated.

    Carb came from Carb-X, p/n 25-935A
     
    dane71 likes this.
  2. Aug 5, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    23,596
    Hi -

    I'm not an expert on the BBD, but I know a little about the "dry bowl syndrome." The 21xx carburetors suffer from that a lot. However, surprisingly my J20's 2150 does not, for some reason. It came to me with a rebuilt carburetor, but I put a kit in the carburetor and followed the settings instructions that came with the kit. It has an intact vapor recovery system (though I'm using an XJ vapor canister), and working TAC (thermostatic air cleaner). The air cleaner closes up tight with the engine off, sealing the bowl vents from the outside air. My J10, which has an open element air cleaner and a 2100, dries out in like a week of sitting. Typical.

    So I would look at two issues regarding the bowl drying out. First if you have an open-element air cleaner, or a TAC that does not close properly, correcting that would reduce evaporation. You also should have a seal between the air cleaner and air horn. The body gaskets in the carburetor should seal the bowl. The float bowl is not meant to drain on its own. Fuel is normally pulled up out of the bowl - fuel exits through the jets at the bottom, it then goes up to exit the idle, main or booster circuits. The accelerator pump well is staying wet, so there's something different about the float bowl.

    There is a 1979 manual here JeepĀ® Parts Manuals online - whoever transferred this used Acrobat to index all the chapters, which is pretty nice. You can click on the section then chapter to go right to the chapter of interest. I suggest you download the complete book. The chapter on the BBD seems quite thorough.

    The ultimate cure for this is to replace the mechanical fuel pump with a quality electric fuel pump. There are safety issues with an electric pump - the easiest way to deal with this is to use an electronic fuel pump controller. Amazon.com: Revolution Electronics Electric Fuel Pump Controller. Primes the pump on key-on and turns the pump off if the engine stops.: Automotive An oil pressure safety switch is another alternative. This can be wired so the pump is on while cranking, and on while there is oil pressure, and off otherwise.

    Fuel injection is another alternative.
     
    Last edited: Aug 5, 2017
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