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  • Carburator Adjustment

    I am pretty sure my carburetor runs too rich, exhaust is black on the exit and smell more and more. I would like to make a basic adjustment until I have a chance to have it professionnaly checked and adjusted.
    I adjusted another car with fully closed plus 2.5 turn or something like that. What can I do there?
    Last edited by Eric S; June 3rd, 2019, 07:55 AM.

  • #2
    2.5 turns is way too much. No wonder it's running rich. You need to use a vacuum gauge to get an accurate adjustment. Hook the gauge to a vacuum source. Adjust one screw at a time. Turn clockwise until the engine begins to misfire. Then turn counter clockwise until the highest vacuum reading is reached. At that point turn clockwise slightly until the reading just begins to drop. Repeat on the other screw. You can also use a tachometer but I prefer a vacuum gauge.

    John
    John Pizzi - Squarebirds Administrator

    Thunderbird Registry #36223
    jopizz@verizon.net 856-779-9695

    http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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    • #3
      It was maybe 1.5 turn....
      The 56 was at about 1.5 but without any ball park number of turn to start with I will use my vacuum gage that I never used. Got it to adjust my Cobra carb but never been able to have any read on it.

      Hope I can find a plug for it. Do I have to use the same vacuum source for both screw or each side has its own?

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      • #4
        Any engine vacuum will work. Most times I disconnect the power brake hose and use that port on the intake manifold. Both mixture screws use the same vacuum.

        John
        John Pizzi - Squarebirds Administrator

        Thunderbird Registry #36223
        jopizz@verizon.net 856-779-9695

        http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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        • #5
          John
          checked on the carb and can not find any place where I can plug my gauge.
          I don't seem to have power brakes.

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          • #6
            The vacuum port would be on the intake manifold, not the carburetor. If you don't have a vacuum port on your intake then you will have to use some other method to tune your carburetor such as a tachometer.

            John
            John Pizzi - Squarebirds Administrator

            Thunderbird Registry #36223
            jopizz@verizon.net 856-779-9695

            http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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            • #7
              The rectangular br*** block on the back of the carburetor is the source for manifold vacuum. You can remove the vacuum line going to the fuel pump from the block and attach your vacuum gauge there.

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              • #8
                I used the set up below.
                I did not used the hose going to the fuel line as I need ot have the engine running (!?) so I used the other one going to the distributor.
                Had a read of 25-27.
                When screwed in the screws, the engine stops of course.
                But when I take them back, needle goes right away to 25-27 and do not move with any screw adjustment? $RCX52CO.jpg

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                • #9
                  You should not disconnect the distributor line. The line to the fuel pump is only for the vacuum wipers. It has nothing to do with the car being able to run. Use that one instead.

                  John
                  John Pizzi - Squarebirds Administrator

                  Thunderbird Registry #36223
                  jopizz@verizon.net 856-779-9695

                  http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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                  • #10
                    Will check again tomorrow morning. I guess however that the second (rubber covered) line entering the square br*** comes straight from the fuel pump / filter / line.

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                    • #11
                      I was wrong again It was well the wiper line. I used it and had more positive results. Although it is not easy to read the effects of the screw adjustments on the needle.
                      I ended up with the screws adjusted 1/3 and 1/2 out from bottom. Is that possible??

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                      • #12
                        Smaller adjustments like you indicated can mean that your mixture screw/needles are worn. If you take one out you will see that they taper to a sharp point. When they get worn they don't seal as well and will be harder to adjust. 1/3 and 1/2 are very small adjustments but if that's what the gauge is telling you and the car is running smooth then I would go by it. Did you do the adjustment with the air cleaner in place. If you didn't you may find out that it's running too lean. The adjustment should be done with the air cleaner on.

                        John
                        John Pizzi - Squarebirds Administrator

                        Thunderbird Registry #36223
                        jopizz@verizon.net 856-779-9695

                        http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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                        • #13
                          With the air filter on, I ended with even smaller openings.
                          I took off both screws and they are sharp and clean. I did not dare to blow air in their holes though so I am not sure if they are clean.
                          I will leave it until I have it checked by somebody that knows.

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                          • #14
                            The Holley 4000 series carburetor service manual denotes 1 turn backed off from tight as the starting point for the mixture screws adjustment. I have done a few that ended up being a less than 1 turn. I agree with the previous post that if the idle is good leave it at that.

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                            • #15
                              It should not have anything to do but after adjusting the 2 screws, now the acceleration is good. Prior to that the car was not accelerating when requested but had a second or 2 delay.
                              Now I have to investigate where all this oil goes. Oil level goes down with no leaks (well no big leaks) and no smoke...

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