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initial mixture screw setting carter bbd

Discussion in 'Intermediate CJ-5/6/7/8' started by gajeep, Aug 17, 2006.

  1. Aug 17, 2006
    gajeep

    gajeep New Member

    Dacula, GA
    Joined:
    Feb 8, 2006
    Messages:
    48
    Hi, I have a carter 2 bbd on a 78 258. Does anyone know approximately how many turns out from lightly seated the mixture screws should be? My jeep is running rich on idle, the screws are 4 turns out; which seems to rich to me. I dont have a digital tach to do the setting correctly and didn't want to play with it until I verified that this is probably rich. It smokes black a little on idle and less when warmed up. If anyone could help I would be thankful. Rob
     
  2. Aug 17, 2006
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
    Joined:
    Sep 20, 2002
    Messages:
    9,221
    I start at 1.5 turns and adjust from there.
     
  3. Aug 17, 2006
    thall

    thall Member

    Joined:
    Jan 30, 2006
    Messages:
    52
    Is your float level correct?
    Do you have vacuum leaks?
    Is your idle speed correct....
    Is your timing correct?
    Is your dwell correct?

    these are just a few things to check that can influence idle quality...

    you don't really need a digital tach... an analog would do also.. but...

    you can adjust the idle mixture by ear...

    or if you have a vacuum gauge even better...

    slowly turn each screw in until the engine stumbles... then back out just until it smooths out.......

    that should get you in the ball park at a fairly lean setting......

    Personally, I think four is too much... I have always started with between 1.5 and two turns out from lightly seated on any carb...

    the ones with reverse idle circuits will get you though... on those you are adjusting the air.... not the fuel........

    good luck.

    i see sparky has also replied.....
    .
     
  4. Aug 17, 2006
    gajeep

    gajeep New Member

    Dacula, GA
    Joined:
    Feb 8, 2006
    Messages:
    48
    Sounds like I have it far to rich. The carb was set like that when I purchased the jeep. I completely rebuilt the engine and everything else for that matter...hahah and have just now begun to drive it around. Everything off idle seem to run perfectly, just that idle richness gives me trouble. I just rebuilt the carb and was very meticulus on the measements. All the adjustments are good, float, idle, and timing. I pluged all unused vacuum lines and I don't have points(engine has been swaped for a 78' model).
    I should turn the screws equally, correct? Also, do you think I should replace the plugs before I adjust since they are problably partially fouled?
    Thanks Rob
     
  5. Aug 18, 2006
    cj-john

    cj-john Member

    Galveston, IN.
    Joined:
    Aug 9, 2006
    Messages:
    242
    Rob, unless you do a lot of idling the plugs should clean up when you are driving. 1.5 turns is always a good place to start but you may need to tweak it from there.
     
  6. Aug 18, 2006
    MA74CJ5

    MA74CJ5 Member

    Bolton, MA
    Joined:
    Oct 28, 2004
    Messages:
    482
    One thing you said is that it smokes a little on idle and less when it warms up. Check your choke setting to make sure you are not too rich. When you are sure that is right move on to the idle mixture screws. Make sure engine is fully warmed before touching the screws. I agree your plugs are prolly fine no need to change.
     
  7. Aug 18, 2006
    NorCoJeeper

    NorCoJeeper Member

    Ft. Collins CO
    Joined:
    Feb 10, 2006
    Messages:
    470
    You don't need a tach to set idle screws, all you need is your ear. Get the engine warmed up by whatever means necessary. Set the screws at 1.5 to 2 turns. While listening to the engine, turn each screw in until the engine runs rough, then back out until it's smooth again. Make sure you adjust the idle speed after every adjustment (you can tell 800 rpm or so by ear.) Do this two or three time, each time adjusting both screws (if it's a two barrel). Once you're at that point, you can turn each one in about 1/8 turn to sweeten the exhaust up a bit. If you have a one barrel, just adjust that screw as described and set the idle speed.

    BTW, this procedure assumes correct float level, no vacuum leaks, timing set correctly, etc, as noted in the other posts. Idle mixture is the last thing you set during a tune up.
     
  8. Aug 18, 2006
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
    Joined:
    Sep 20, 2002
    Messages:
    9,221
    What NorCoJeeper said, except I prefer to use a vacuum gage now rather than just by ear. Tune for maximum vacuum.
     
  9. Aug 18, 2006
    gajeep

    gajeep New Member

    Dacula, GA
    Joined:
    Feb 8, 2006
    Messages:
    48
    Thanks for all the help everyone. I did the adjustment and the jeep runs much much better. It's very smooth now at idle and no smoke at all, much quicker throttle responce as well. Off the line is doesn't hesitate or bog either, it did slightly before.
    I bet the guy I bought the jeep from had adjusted the screws incredibly rich so it would idle since the engine was shot; had to have it bored .060" over, it still ran decent somehow but I had noticed a skip that I just counldn't iron out. She runs perfect now though!!! Thanks again everyone! Rob
     
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