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Holley carb idle adjustment screw

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  • Holley carb idle adjustment screw

    2001 Volvo Penta 3.0 GSM-A with Holley carb. I adjusted the idle mixture screws for best rpm/vacuum reading. The rpms increased as screws turned in (leaner) from the starting point of 1.5 turns out. Both screws now sit about 1.0 turns out. I can't slow the idle down with curb idle screw. The curb idle screw is all the way out and no longer contacting the throttle stop on the linkage.

  • #2
    Adjust your Throttle linkage to allow the throttle blades to close Against the stop . Look back on the throttle linkage should be be a barrel nut back thee to adjust


    • #3
      I'm confused. A barrel nut and a curb idle screw on the throttle linkage to set idle speed? Where is this barrel nut?


      • #4
        Here are photos of the throttle linkage. I do not see the "barrel nut" you speak of. Sometimes when you turn the idle speed screw all the way counterclockwise and engine does not slow, it is indicative of a vacuum leak. However, I am unable to locate any vacuum leaks. Advice and suggestions welcome.


        • #5
          If you take out the cotter key and remove the throttle cable, do the rpms come down then? if so, you need to loosen the little nut at the base and turn out the arm a turn or 2 to close the throttle plate. If the plate is already closed and no adjustment is required and you have no vacuum leak, then I would suggest you check the timing? Over advanced will bring the idle up.


          • #6
            Where would you look for typical vacuum leaks? I tightened the carb base. Seems to be only 1 small vacuum hose from front of carb to choke area.


            • #7
              Please do what Senior B posted then let us know. It sounds like the throttle linkage needs to be adjusted as its giving some input


              • #8
                I didn't realize you were talking about the nut on the throttle cable (not throttle linkage). Yes, I have adjusted the trunion at end of the throttle cable to apply preload to close the throttle. Even with:
                1) curb idle screw all the way counter clockwise and
                2) throttle cable preload to close throttle
                it will not idle down below 1000 rpm and diesels.
                Are the factory tachs reliable on these Volvo Penta 3.0L engines?
                Perhaps vacuum leak? - which I can't find.
                Or maybe timing? - which I don't know how to measure/adjust do on this new-to me 2001 SXM-A.


                • #9
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                  Go thru the carb. If you damaged the power valve, it will not idle properly.
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