Throttle linkage geometry

Fuel and Air Systems

  1. dusterbd13

    dusterbd13 Well-Known Member

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    So, i went back to a carb from multiport fuel injection.
    I kept the lokar throttle cable and bracket.
    Car is a 70 duster, 360 with a manual transmission and a double pumper.
    I can only get 3/4 throttle no matter how i set it up.
    I am using the holes on the Holley carb linkage, no adapters or anything. Didn't think they did anything except for transmission control on an automatic.

    Before I spend money on the mopar specific adapter, im wondering if theres something im missing. Almost has to be, but i can't see it. Pedal hasn't changed, throttle cable through the firewall hasn't changed, only the engine end.

    Also, if someone has a template or drawing fir a linkage adapter isi can make, im all eyes!
     
  2. toolmanmike

    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    Post a photo or two of what you have and may be we can help.
     
  3. 694spd

    694spd Well-Known Member

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    To get more throttle plate travel for the same amount of throttle cable travel. You would need to move the connection point of the throttle cable closer to the pivot point of the carb's throttle shaft.
    I hope that makes sense. It usually means picking a throttle cable connection point "lower" on the carb's linkage.
     
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    • threewood

      threewood Well-Known Member

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      You need holes that are not on the Holley linkage. You are better off buying the adapter from Holley. It is $11.48 through Summit, # 20-7

      I recently went TO efi (Holley Sniper) and I modified a plate I had for the linkage (stock throttle cable +1", Bouchillon trans cable)
      The bottom hole on the Holley linkage works perfect to get full arm swing at the trans.

      Here is where I put my throttle after experimentation. The plate I used was from Bouchillon. Full wot verified.
      20201216_175252.jpg
       
    • abodyjoe

      abodyjoe Well-Known Member

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      got a picture of how you have it set up? i've been using lokar throttle cables for many years and have never had any issues getting full throttle with a holley and no adapter brackets..
       
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      • abodyjoe

        abodyjoe Well-Known Member

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        Here is my set up. Just ran out and took the picture. Performer rpm intake and 650 double pumper. I even have a little slack in the cable ( big mistake not having any that many people make) and easily get full throttle.

        IMG_20210108_093127.jpg
         
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        • dusterbd13

          dusterbd13 Well-Known Member

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          20210108_144936.jpg
          I seem to be using the same hole as abodyjoe. However, i am only getting 3/4 throttle or so. Not really any holes to go down more, either. And looking at the adapter, it seems it places the connection point for the cable between where i have it and the big hole, making for LESS travel.

          Or am i being dense somehow?
           
        • Mike69cuda

          Mike69cuda 66 is the new 17 FABO Gold Member

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          Make sure your carpet isn’t too thick under your pedal. I bent my pedal up to get more travel.
           
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          • toolmanmike

            toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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            Look at Joe's linkage. Could you get more travel here?

            linkage2.jpg
             
          • 694spd

            694spd Well-Known Member

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            Is there any slack in the throttle cable when the carb is at idle?
            You want just a slight amount of cable slack at idle. Any more than that
            can reduce the amount of full throttle that you can get.
             
          • abodyjoe

            abodyjoe Well-Known Member

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            Sure the cable was cut the right length? Is the inner cable pulled lifting the pedal the right way? Carpet like stated mat be keeping the pedal from traveling enough. It has to be something really stupid.
             
          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            Here's another way you might think about going. Without changing "the whole thing" that is leaving the pedal and cable setup alone, to get more movement you need to move the cable attachment at the carb closer to the throttle shaft, PERIOD.

            BUT..........on newer cars, many linkages use a "partial pulley" that is they wrap the able around a "drum" section so that it ROLLS back. And this prevents the linkage from changing ratio as it moves. That is, as the conventional throttle lever on the carb moves, it has a faster ratio until the cable becomes at right angles to the lever....and then the ratio slows lever movement, and as it continues towards further open, and the angle again increases, the ratio speeds back up. This "pulley" type deal prevents that action

            Like this

            16622.jpg
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            You only have two choices, move the carb end closer to pivot, or bend the pedal up higher. It's real simple geometry. Well I suppose you could move the cable to pedal attaching point, further from the pivot....... but then it won't go thru the firewall in the factory location.....

            I too have a 750DP on an AirGap, on a 360, with a 70 Duster pedal in a 68 Barracuda. But with a factory cable.
            I am using the Holley/Mopar adapter, and I did have to bend my gas pedal up a tad higher.
             
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            • abodyjoe

              abodyjoe Well-Known Member

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              May be able to adjust the lokar bracket on the carb some too.
               
            • dusterbd13

              dusterbd13 Well-Known Member

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              Ill need to check carpet and make sure, but i doubt it.

              HOWEVER, the thought that just woke me up from a dead sleep is wondering if the munchkin had long enough legs! I need to get the wife to check when we get home tomorrow. I may be chasing a problem ive already fixed.

              And yes, slight slack at idle. Also, ive gotten all the travel i can from the factory pedal without major bending bu moving the tab behind the pedal that acts as a stop for closed throttle. That got me a lot of travel, as before i was barely getting the secondary side open
               
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