Six Pack outer carb vacum ?

Fuel and Air Systems

  1. Mikke H

    Mikke H FBBO Gold Member FBBO Gold Member

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    At what point shall there bee vacuum to the outer carbs i tested the vacuum port at idle no vacuum tryed to rev but same result is there vacuum only under load ?
     
  2. Demonic

    Demonic Well-Known Member

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    Correct. Should not be there at idle. The air passage is to the venturi. The air velocity through the center carb would need to be somewhat sustained. A fabricated 1/4" pipe tee to barb fitting attached to your compressor air hose can make a "jet pump" - similar to a siphon. You can attach each outboard to the bullhead on the tee and verify with the engine off.
     
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    • R/T Boy 67

      R/T Boy 67 Well-Known Member

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      The vacuum is created by air flow through the center carb, same as a four barrel. There won't be any at idle, or by blipping the throttle.
       
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      • R/T Boy 67

        R/T Boy 67 Well-Known Member

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        Typing at the same time.
         
      • Mikke H

        Mikke H FBBO Gold Member FBBO Gold Member

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        Ok how about this long hose into the car and hammer it there shoud bee a vacuum signal at 2500 or so ?
         
      • 62MAX

        62MAX Well-Known Member

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        You're starting to scare me !!
         
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        • 66Satellite47

          66Satellite47 FBBO Gold Member FBBO Gold Member

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          Vacuum is generated by air flow through the center carb. To check the end carbs action, suck on the hose, see if they react.
           
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          • BSB67

            BSB67 Well-Known Member

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            Kinda thinking the same thing.
             
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            • Mikke H

              Mikke H FBBO Gold Member FBBO Gold Member

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              Yes they act but i dont feel any kick just a smooth transition upp too 5500 to 6000 grand nothing exiting looking for tiresmoke vibration black tire marks and sutsh MOPA
               
            • R/T Boy 67

              R/T Boy 67 Well-Known Member

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              A good real world test, is to tie some yarn or a twist tie around the shaft from the vacuum canister and push it up tight against the housing. Make it just tight enough to stay put, and then go for a blast. If the secondaries are opening, the yarn will be down on the shaft the same amount as they opened. You might have to change the diaphram springs.
               
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              • Mikke H

                Mikke H FBBO Gold Member FBBO Gold Member

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                Will do !
                 
              • 62MAX

                62MAX Well-Known Member

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                just a smooth transition upp too 5500 to 6000

                This is how it is supposed to work !! If you want "kick",change the springs,you may find your expectations are not what you expect !!
                 
              • 66Satellite47

                66Satellite47 FBBO Gold Member FBBO Gold Member

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                Smooth is what I want. But change the end carb springs to get sooner opening.
                 
              • Mikke H

                Mikke H FBBO Gold Member FBBO Gold Member

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                Ok now this is my new set off carbs they are bone stock unmolested set ,the set that came whit the car had a different mode off operation they gave a clear kick att about 2500 rpm and i asumed that is how they work !So what you are saying is that smooth is how they are setup from start ?
                 
              • 66Satellite47

                66Satellite47 FBBO Gold Member FBBO Gold Member

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                Try the different end carb springs & see what you like.
                 
              • rarefish

                rarefish Well-Known Member

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                If the outboards come in too quickly, you will get a bog. Remember there are no accelerator pumps in the outboard carbs. That is why the transition has to be a little slow.
                 
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                • BSB67

                  BSB67 Well-Known Member

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                  Generally speaking, if you take your stockish street car to the track, and experiment with outboard carb opening rate to achieve the lowest et and hightest mph, you will find that there will be a very noticeable surge when the outboard carbs come-in on the street from a roll. We've proven this time and time again. And conversely, if you slow down the outboards so that there is no noticeable surge with WOT from a roll, you just slowed the car down probably .3 sec, and 2 mph.
                   
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                  • Mikke H

                    Mikke H FBBO Gold Member FBBO Gold Member

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                    Ok thanks for all tips i wont start to fiddle with the outer carbs stock is god inuf for me just vanted to know how the sekonderies vas ment to operate .
                     
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