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Dauntless bog at speed

Discussion in 'Early CJ5 and CJ6 Tech' started by RyanKnol, Apr 15, 2016.

  1. Apr 15, 2016
    RyanKnol

    RyanKnol New Member

    BC, Canada
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    Jan 20, 2014
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    So i have the jeep running awesome. fires up easily, idles perfectly, loads of power, etc.

    its an hei at about 6-7 deg adv. no air leaks that i can find, but one day there was a small seepage of fuel from passenger side of the bottom butter fly rail. i might need to seal or sleeve that somehow.

    the main problem is. at cruse speed. in 4th, (t98), the jeep stumbles slightly. and bogs for a second when ya step on it. If i pull the choke most of the way, it goes away and drives perfectly!

    so keep in mind im somewhat new at carbs, im assuming the jets are too small? im at ocean level, with some mountain climbs. what jet should i have? maybe drill out the current one? am i missing something?

    thanks for any help! i love this place
     
  2. Apr 15, 2016
    tarry99

    tarry99 Member

    Northern California
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    What color are the plugs? What type of carb is this 2 barrel or 4?............Sounds rich to me as when you close the choke blade in effect your restricting air which should lean the motor. Now it could also be an accelerator pump? Float level?.........is there any advance system in the HEI .........vacuum or centrifugal?

    Once you get beyond the point where it stumbles , can you then open the choke blade up all the way?
     
  3. Apr 16, 2016
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
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    Was this happening while running or after shut-down? Answer tarry99's questions and we can go from there. Also would help to know your total advance with the HEI.
     
  4. Apr 16, 2016
    RyanKnol

    RyanKnol New Member

    BC, Canada
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    Jan 20, 2014
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    ill have to pull the plugs, its a 2g carb, rebuilt a year or so ago, the accelerator pump works fine. with the choke pulled out a bit the jeep runs great. float level "should" still be ok.

    yes its an hei, set to about 6-7 adv, there is vacuum hooked up. and i believe centrifugal working as well. cant really tell where the timing marks get to as my light is hard to get in there. but im guessing around 20+ when at about 2k rpm. ill have to double check.

    it only stumbles slightly when cruising. ill pull the choke a bit and it goes away and runs perfect. push the choke back in and it starts again instantly.

    i checked where the choke is when it runs best and it is just covering the venturis

    So if its running rich at speed. im assuming swap out the jet? whats a good size?
     
  5. Apr 16, 2016
    PeteL

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

    Hills of NH
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    I'm confused. :n:
    Wouldn't giving it choke enrichen the mix... which would mean the carb is running too lean?
     
  6. Apr 16, 2016
    Focker

    Focker That's a terrible idea...What time? Staff Member

    WA
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  7. Apr 16, 2016
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    That's what I thought too. o_O
     
    47v6 likes this.
  8. Apr 16, 2016
    colojeepguy

    colojeepguy Colorado Springs

    At the foot of...
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    You are correct.
     
  9. Apr 17, 2016
    tarry99

    tarry99 Member

    Northern California
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    Sorry PeteL , Your not confused you are right...........but I was covering a lot of ground in that reply.......Ie; Color of plugs? type of carb, accelerator pump, floats, and perhaps even ignition?

    Chokes obviously used at startup or Idle will no question richen the motor...........but at higher RPMs that may not always be true if you subscribe to Bernoulli's Principals of fluid moving whereby sometimes pressures are on the increase or decrease.

    By closing the choke blade down a little at various throttle positions it can help to determine if there is an RPM range that either needs more or less fuel..............

    Most flat spots , stumbles or hesitations when the pedal is floored is caused by a big gulp of air that drops manifold vacuum and of course air velocity.........A correctly working accelerator pump should mask that somewhat?

    The truth is that most carburetors have a hard time mixing an air/fuel ratio of about 12-13 to 1 or Stoichiometric mixture of 14.7 to 1.............Notwithstanding the variables present in an Odd-fired motor................Sorry for the confusion.
     
  10. Apr 17, 2016
    PeteL

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

    Hills of NH
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    Jeez. o_O

    I think you forgot to mention the Coreolis effect... :rofl:
     
  11. Apr 17, 2016
    Willys43

    Willys43 Member

    Kansa City
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    Could be a slightly restricted fuel filter. How old is yours?
     
  12. Apr 17, 2016
    tarry99

    tarry99 Member

    Northern California
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    Coreolis ? Sure add that in if you like(y)..................Where I was going is that most carburetors at WOT and higher RPM's will richen the motor.......this is due to the fact that the time to process fuel becomes shorter as well as the trapping time in the cylinders also becomes shorter for each firing event........on the race track with say the Holley 4500's we use a series of air bleeds in the circuits to lean the charge to compensate for that....

    I think that Ryan who was first asking about his engine stumble has to go look at all of things that can act as part of the problem..........not an easy fix most times.
     
  13. Apr 17, 2016
    Willys43

    Willys43 Member

    Kansa City
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    I had an old Ford pickup that had crap in the fuel tank. I knew the filter was getting full because I could drive normally until I get to a hill and the additional load would cause it to start coughing and sputtering. I'd pull over and put a new filter on it and off I'd go. Couple of months later it would happen again.
     
  14. Apr 19, 2016
    RyanKnol

    RyanKnol New Member

    BC, Canada
    Joined:
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    20
    clean filter on it, fuel and tank are pretty clean.

    runs fine climbing hills, engine lope/popping when idling down a hill or if i let the rpms slow me down.

    i figure its running lean. just wondering what jet size is normal for ocean level?

    thats probably the easiest thing to diagnose, no?

    dirty power valve could make sence but it was all cleaned last year or so.
     
  15. Apr 19, 2016
    tarry99

    tarry99 Member

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    Put a New set of plugs in it ..........drive it like you stole it for a day in the RPM range where you have trouble and see if they color? If there dead white and no color on the porcelain then perhaps it is lean......... if there is brown on the porcelain that's residual un-burned fuel..........

    Popping w/throttle off under compression normally means you have un-burnt fuel going out the exhaust valve / pipe that is re-igniting in the pipe...........did you ever correctly check your timing? Both at Idle and at RPM?...............have you done a leak-down test on the cylinders yet?...................your looking for the easy answer but that is not always the case.
     
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