cant get the idle down

Discussion in 'Fuel and Air Systems' started by purplescamper, Dec 6, 2018.

  1. purplescamper

    purplescamper Well-Known Member

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    I have a 360 with a thermoquad carb on it, no matter what the timing is or how I set the curb idle screw I cant get it to go any lower then 1500 rpm...any ideas ?
     
  2. joshcook81

    joshcook81 Well-Known Member

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    The tach might be messed up
     
  3. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    Possible vacuum leak?
     
  4. ScampMike

    ScampMike Despicable Damn Yankee FABO Gold Member

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    improperly installed or adjusted throttle cable?
     
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    • Bad Sport

      Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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      Can you post a pic from the throttle side?
       
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      • Frnknsteen

        Frnknsteen FABO Gold Member FABO Gold Member

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        That's the first thing I would check. I pulled my intake off to do some work. When I put it back on, I apparently didn't get the throttle mounted back on the same way. When I started it, it was running about 2500 rpm and there was tension on the throttle. Adjusted the cable and it was fine.

        Other thing I would check is to see if something is holding the butterflies open. What were you doing, or working on when it started having the issue (have the carb off?)
         
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        • AJ/FormS

          AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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          Check to make sure the primary butterflies are completely closing, and not hanging up on the fast-idle cam. Then make sure the secondaries are also closing, simultaneously. If the engine continues to run, it's getting BOTH air AND fuel, so it pretty much has to be coming past the transfer slots.......
          If it continues to run with all 4 butterflies fully closed, Ima thinking the mainwells are leaking. TQs are known to do that.
          If you had the carb apart and replaced the gasket under the bowls, be advised there are at least 4 of those gaskets that I have seen, and perhaps you installed the wrong one.
           
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          • MoparMike1974

            MoparMike1974 Well-Known Member

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            Look at the carb butterflys to see if they are fully closed. Disconnect throttle cable and check again. If that's not it I would start looking for vacuum leaks.
             
          • purplescamper

            purplescamper Well-Known Member

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            should be good...I had scott smith rebuild it
             
          • rustycowll69

            rustycowll69 Well-Known Member

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            I've never SEEN it done, but I suppose it could be done. Maybe somebody used the wrong gasket (smaller (800?) gasket on a larger (850?) carb) between the bowl and the throttle body, and it is preventing primary throttle plates from closing fully
             
          • AJ/FormS

            AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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            "Should be good", start it up and drive then.

            The carb might be good
            But you still got to install it and check stuff.
            Several guys have already said what to check, one of us or all of us are bound to be right.
            It could even be that one of the primary valves has slipped in the throttle shaft. You just gotta pull the carb off, flip it over and look. Until you look, and don't find any of the valves hanging up, we're all guessing,
            And in all honesty; I know of no way for both air AND fuel to enter the intake in the right proportion to support 1500 rpm..... with all 4 valves fully closed.
             
            Last edited: Dec 6, 2018