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  •  » Carb tuning / vaccum at idle

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    4/06/2021 9:00 PM  #1

    Gaba
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    From: Van Alstyne Texas
    Registered: 1/15/2014
    Posts: 1,009

    Carb tuning / vaccum at idle

    Ok, I have a question : summit carb 600 with vaccum advance (new, 30 miles old)
    Engine is Ford 347 new build , 50 miles old

    I set the throttle butterfly as in shown in many videos (square transfer slot) , ignition timing at idle 12 degrees advance .

    Idle screws set to 1/2 to 3/4 turn from factory. Seemed low but ok.

    Car will not idle at the butterflies being where the transfer slots are square, it has to be screwed in 2 turns to get it to idle at 900rpm or so , in drive (automatic) maintaining 600 or so rpm

    What would you do to make the engine idle at the optimal setting of the curb idle screw ?

    Vaccum is hovering at 15 inches at idle in Nuetral, and bounces like crazy in gear .

    All that to say, I need help setting up this engine right. All spark plug wires checked and rechecked , faulty ones remade new. Engine is running smooth enough but new engine with 15 inches at idle seems low.. also seems like a result of the curb idle being open too much..

    MSD distributor, MSD 6AL, MSD coil, no vaccum advance setup. All vaccum ports blocked .

    Cam :: Howard’s cam

    221275-12 270/278  217-225 (1400-5600 rpm)  0.528" / 0.533" LSA 112

    Compression : 9.5:1

    So help please .. is 15 hg vaccum too low for a new engine?

    I have tried to set the idle mixture screws by vaccum gauge . And at this idle curb setting I have them where I have most vaccum ::15

    If it aint broke, I have'nt tried to "Fix" it yet!
     

    4/06/2021 9:18 PM  #2

    6sally6
    Hyper FYIFORD ADDICT

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    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,853

    Re: Carb tuning / vaccum at idle

    UR sure..........there are NO vacuum leaks!?
    Try this:.........plug vac advance  and give it more initial advance. (14-16*) see if that increases your idle enough to turn down your curb idle. It should. (give the engine what it WANTS...knot-watt da book sez) Its mechanical...they are all different.

    No vacuum leaks..............right?! (yeah it's that important!)

    Your coming into the home stretch.....you bout got dis thang!!!

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    4/06/2021 9:20 PM  #3

    Gaba
    Senior 24-7 FYI Addict

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    From: Van Alstyne Texas
    Registered: 1/15/2014
    Posts: 1,009

    Re: Carb tuning / vaccum at idle

    Definitely no vaccum leaks .

    No vaccum advance is being used , distributor doesn’t have an option for it .

    I can go to higher idle initial timing .. that’s the only thing left honestly

    If it aint broke, I have'nt tried to "Fix" it yet!
       •Thread Starter
     

    4/06/2021 9:21 PM  #4

    6sally6
    Hyper FYIFORD ADDICT

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    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,853

    Re: Carb tuning / vaccum at idle

    How???...did the pushrods get too short? 050?(IF the heads were milled/shaved the pushrods would be too long)
    6sal6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    4/06/2021 9:27 PM  #5

    Gaba
    Senior 24-7 FYI Addict

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    From: Van Alstyne Texas
    Registered: 1/15/2014
    Posts: 1,009

    Re: Carb tuning / vaccum at idle

    6sally6 wrote:

    How???...did the pushrods get too short? 050?(IF the heads were milled/shaved the pushrods would be too long)
    6sal6

     
    New aluminum heads, new scorpion roller rockers. Measured wrong while building

    If it aint broke, I have'nt tried to "Fix" it yet!
       •Thread Starter
     

    4/07/2021 11:27 AM  #6

    Bolted to Floor
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    From: Houston, Texas
    Registered: 4/01/2013
    Posts: 2,016

    Re: Carb tuning / vaccum at idle

    I am no carb expert, but what if you kick the back barrels open a little more for air and allow the transfer slot as a square. As for the 15" of vacuum, it sounds reasonable to me. 

    John  -- 67 Mustang Coupe 390 5 speed
     

    4/07/2021 11:45 AM  #7

    RV6
    Senior 24-7 FYI Addict

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    From: Pine Junction, CO
    Registered: 3/01/2016
    Posts: 1,248

    Re: Carb tuning / vaccum at idle

    Bolted to Floor wrote:

    I am no carb expert, but what if you kick the back barrels open a little more for air and allow the transfer slot as a square. As for the 15" of vacuum, it sounds reasonable to me. 

    My thoughts as well. Pain to change since the carb has to come off to set the rear plates.
     

    Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
     

    4/07/2021 6:57 PM  #8

    6sally6
    Hyper FYIFORD ADDICT

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    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,853

    Re: Carb tuning / vaccum at idle

    Gaba.......ck your PM's
    6s6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

     

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