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Carb Adjustment(s)

Discussion in '40- & 55-Series Tech' started by scott74_40, Feb 5, 2004.

  1. scott74_40

    scott74_40

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    Just got my stock 6/74 Fj40 back together. Not a rebuild, but a cleanup from the firewall forward. New headers, fuel pump, pcv valve, rebuilt alt & starter etc. etc..... From my inspections I have no vacuum leaks. Everything is sealed up and looking good.

    The truck runs and starts well but with cold starts it has a little trouble idling even with the choke out (to first "click"). The choke does not make the idle increase excessively, it just smoothes out the lower idle (650 rpm) to where it keeps running. On the road, if you hit the gas, it hesitate (no pinging) until it hits a little higher RPM and then it runs great.

    Figured this is a fuel delivery issue (rich - lean??). Sight glass has gas and the acc pump seems to be working.

    I looked at the factory service manual and the archives for carb adjustments. No real help. Anybody have any ideas on ho to adjust the carb to fix these issues.

    Regards,

    Scott
     
  2. Jukelemon

    Jukelemon

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    What type carb?

    There should be two adjustments; idle mixture and idle (rpm). There has to be a "start" setting for your carb in your manual. I know that the tech articles have it for the Weber replacement. But essentially, with any carb, you need to set your idle set screw at a preliminary setting and then adjust the idle mixture just above the stalling point. Then you can set your idle for 650-700 rpm.
     
  3. folsom50

    folsom50

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    Ditto what Juke said, I had the exact same problem after I rebuilt my 2f, so I just started at the prelim. settings on the idle mixture and between that and the idle speed, alot of back and fore adjustments to both got the motor to smooth up and idle really nice.
     
  4. scott74_40

    scott74_40

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    Carb is the stock 2 barrel. Just FYI - I tried adjusting with idle mixture screw. Located at the base of the carb towards the passenger side (pic 2 on link). Turned it in and out an nothing happened. Just tested it to see what would happen.

    http://www.sor.com/sor/catpict.tam?xax=778&itemnum%2Ectx=042%2D01G&itemnumdesc%2Ectx=3%2F73%2D12%2F74%20Federal%20Model%2Dno%20EGR&page%23%2Ectx=042&catpage%2Ectx=cat042%2Etam&pagetitle1%2Ectx=Page%20042&pagetitle2%2Ectx=Carburetion&descriptionpg%2Ectx=Page%20042%20Carburetion
     
  5. IDave

    IDave

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    1 1/4 turn out from fully closed is the starting setting for the carb mixture.

    You should have a fast idle speed adjustment screw, too. It should have you at about 1600 at full choke, IIRC. Certainly not at 650.
     
  6. Jukelemon

    Jukelemon

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    If nothing hapened then something is wrong with your carb. You should be able to completely shut off the engine if seated all the way. Sometimes, if the carb ir original and has not been rebuilt or taken good care of, the idle mixture screw can be at fault i.e. if someone were to seat the screw too tightly not knowing what it is for. But for sure if that mixture screw is not doing something, something is wrong in the carb. As well, your idle screw might be set too high/low or your butterfly could be not seating correctly or is too loose or worn.