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Thread: Carter BBD idle problem

  1. #1

    Default Carter BBD idle problem

    I only get 9 mpg. It smells rich. I have the idle mixture screws turned all the way in. If I back them out it really starts smelling like unburned gas. If I take the passenger side idle mixture screw out completely, the engine runs smooth. no black smoke, lots of power. Like it is finally getting the air it needs. If I put the passenger side screw back in and take out the driver's side idle mixture screw, it stumbles badly.

    I am stumped, any ideas? I rebuilt it twice. Do I just leave the passenger side idle mixture screw out? It runs great that way.

    Carter BBD no stepper motor, 258ci, inline 6

  2. #2

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    Quote Originally Posted by desert_driller View Post
    I only get 9 mpg. It smells rich. I have the idle mixture screws turned all the way in. If I back them out it really starts smelling like unburned gas. If I take the passenger side idle mixture screw out completely, the engine runs smooth. no black smoke, lots of power. Like it is finally getting the air it needs. If I put the passenger side screw back in and take out the driver's side idle mixture screw, it stumbles badly.

    I am stumped, any ideas? I rebuilt it twice. Do I just leave the passenger side idle mixture screw out? It runs great that way.

    Carter BBD no stepper motor, 258ci, inline 6
    WAY PAST TIME FOR A CARB REBUILD!

    Spend the $20 and rebuild the carb, check your choke pull off, ect.

    If your carb looks like this one,



    You will be GLAD you forked over the $20 and fixed things right!

    Same complaints as yours,
    Won't idle (Cause the idle fuel passages were blocked and it was trying to suck off the main jets!)

    And one main jet blocked, not to mention the crud in everything else in there!

    Every adjustment was screwed up (PO) so they wrote the jeep off and sold it cheap.
    We spent some time and money fixing the ignition, carb, cleaning things up and fixing stuff.

    Now we get to break axles/u joints about every weekend in it!
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  3. #3

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    Quote Originally Posted by Junk Yard Genius View Post
    WAY PAST TIME FOR A CARB REBUILD!

    Spend the $20 and rebuild the carb, check your choke pull off, ect.

    You will be GLAD you forked over the $20 and fixed things right!

    Same complaints as yours,
    Won't idle (Cause the idle fuel passages were blocked and it was trying to suck off the main jets!)

    And one main jet blocked, not to mention the crud in everything else in there!
    I rebuilt it but I will do it again and be twice as careful. I must have missed some of the crud hidden in the passages.

  4. #4

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    The choke pull off, that is the electric choke right? It works fine. Opens up in less than a minute.

  5. #5
    Registered Don Stephens's Avatar
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    Default

    When I had my BBD, The stepper motor motor looked way to complex for me so I had it done. That was a good choice as it performed flawlessly. I did have a rich fuel mixture a couple of years later and that turned out to be a bad O2 sensor. That could possibly be the problem that your are having. Replacing all those vacumn lines and new distributor helped also. I got a lot of good info from sites off the net dealing with the BBD and it related computer system. I see that you have stated that you are not using the stepper motor. Are you able to set the richness manually without the use of the computer? Then a "Nutter Bypass" would be nescessary.

  6. #6

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    Thanks Don, I have done the Nutter. My problem is in the idle circuit. Something isn't right. I will pull the carb and rebuild it.

    I am getting pretty good at the rebuild part. I can take it off, tear it down, measure everything, and put it back together. It only took about five years to learn. No one ever said I was quick. But now I would rather rebuild the carb than go four wheeling. It is so technical, I love the little details. Like "Set vacuum piston to .040". Wowzers! What does that mean! And It weighs less than four pounds, so no jack is required. I can do it at home, and when I am hungry the wife is always ready with a hot lunch, and I can take a nap if I want. I can even watch the ball game if I am tired of working on it. Rebuilding the carb is the max.

    BTW, I have replaced all the vacuum lines, it has a new cap, rotor, plugs, wires, filter, EGR, and I have filters on all the lines. Thanks!
    Last edited by desert_driller; 01-25-2010 at 01:27 AM. Reason: re read post

  7. #7
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    I got rid of the BBD (for idle issues) for a mc2100 and aint going back!

  8. #8

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    I went the MC2100 route, had lots of problems, so I am back with the carter. Thanks.

  9. #9
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    clean the idle tubes.

  10. #10

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    Clean the idle tubes, then clean the fuel lines to the carb.
    That first flush through the lines will surprise you on what comes out!

    Did you, by any chance, replace the inlet valve when you did the rebuild?

    If so, did you take a float height measurement before you took the old valve out?

    AND I AM HOLDING THE FLOAT FULLY UP IN THIS PICTURE...



    New valve will NEVER be close to what you need..
    Don't ask me why, but I've never seen a rebuild kit for the BBD that put the float level anywhere near where it needs to be stock.

    Did you take the throttle blade linkage apart?
    If so, that stuff is VERY hard to get back together again correctly.
    Most of the time you should just clean it in place and not disassemble.

    If you uncovered the transfer slot, you will have EXACTLY the same symptoms as you describe since you will be pulling off of main jets instead of idle circuits.

    Make sure your throttle valve (Blades) are closing fully, then adjust the curb idle stop/idle speed from there.
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  11. #11

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    I did replace the fuel intake needle and seat. I did noticed that the float didn't reach the same height as before so I adjusted it. What is the transfer slot?

  12. #12

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    Quote Originally Posted by KEVINS-7 View Post
    clean the idle tubes.
    I did that, that was one of the first things. Thanks!

  13. #13
    Registered Don Stephens's Avatar
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    Here is how to clean out the idle tubes, plus open them up a bit with a drill. I did it with a hand chuck:
    http://www.jeeptech.com/engine/carter.html

  14. #14

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    Transfer slots are the vacuum transition slots in the venturi body that smoothly allow transition from idle circuits to main jet circuits.
    They are a small slot in the throttle bores.
    You should see one small round hole just above the base plate mating surface for the intake,
    Then a small vertical slot. That is the transition/transfer slot.

    This is a picture of a Holley, but most carbs look the same.



    If you get the throttle blade open far enough to put vacuum on the transfer slot, then you will start disabling the idle fuel supply and start drawing off the main jets WAY too soon.
    REMEMBER!
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  15. #15

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    I see them. I saw those in the Carter too. " If you uncovered the transfer slot"" Ok that means if I opened up the butterfly right? I didn't mess with it. Right now the transfer slot is about 70% upstream and 30% downstream.

    Thanks, JYG!

  16. #16

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    Yup, the more of the transfer slot you uncover, the more your carb will pull off main jets, and the less actual idle mixture you will be running on.

    You don't have enough air moving through the carb for mains to function properly, so you get raw drips of fuel instead of atomized fuel in the air stream.

    Adding air through the idle mixture screw would do two things,
    One, lean it out a little since when the screw is removed you are just delivering air and no fuel from idle mixture,
    And two, leaning out the mix a little so the 'drops' burn a little cleaner.

    Raw liquid fuel doesn't burn efficiently, so you get the smell of raw fuel out the exhaust,
    With some air, and it will run a little better, but you still aren't 'Right' by any means.

    Check the float level, check the idle speed adjustment, and if that doesn't fix the 'Issue', it's time for a GOOD CLEANING and rebuild!

    The one thing I see guys do over and over again is try to blow through the passages from the SUPPLY SIDE.

    You should blow BACKWARDS from the delivery side to dislodge particles from the smaller passages to the larger ones,
    Instead of pushing the particles farther into ever DECREASING size passages...
    That's a bad thing to do, but it doesn't occur to a lot of people the passages get A LOT SMALLER as the fuel gets farther into the carb.
    Last edited by JeepHammer; 01-26-2010 at 12:39 PM.
    REMEMBER!
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    ----------------
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  17. #17

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    Thanks JYG,

    OK, I rebuilt the carb and this time I doubled my efforts to do it right. Used lots of carb cleaner. It idles much smoother. No stalls at stops. Starts up first thing in the morning. It doesn't smell like unburnt gas anymore.

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