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Old 12-26-2019, 03:39 PM
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SD421 SD421 is offline
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Default Mixture Screws Over 3 Turns Out

Hi again,
Another question:

So my mixture screws are over 3 turns out and I already opened the Idle Orifices and the Mixture Screw holes up per Mike Wasson's recommendation.

If I want to be 2 turns out or less, do I need to open them up just a little more?

Thanks,
Don

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1966 GTO

1966 421-9.3-1 comp-Race Tec 23cc Pistons
1966 Tri-Power
1967 670 Heads
Pontiac "Highlift" TriPower Cam by SpeedPro
DUR 214 Int 224 Exh @.050 - 107 ICL
LIFT .445" Int .465" Exh
Tri-Y-Headers by Tribal Tubes w/ Goerlich Mufflers
1966 Muncie Wide Ratio 4-Speed
1968-72 Chevy 12 Bolt Rear End w/ 3.73 rear gears
  #2  
Old 12-27-2019, 12:41 AM
Goatracer1 Goatracer1 is online now
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If it runs good why worry about the screws?

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Old 12-27-2019, 06:05 AM
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Kenth Kenth is offline
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Idle channel restrictions? Std is .046", you may open them to .050" for increased amounts of idle mixture to the idle screws.
Also, 1966 Tripower center carbs uses idle screws with a shorter needle (steeper angle) than earlier Tripowers, check for the correct ones.

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Old 12-27-2019, 09:21 AM
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Sirrotica Sirrotica is offline
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To be perfectly truthful, idle mixture screws aren't adjusted by counting turns. The correct way to adjust them is with a tach and observing how smooth the engine is idling.

It takes a few minutes to keep going back and forth from one to another with minute adjustments to get a really smooth idle, but when they are right, the idle is smooth as silk.

I'm not sure where the counting turns thing came from, but it's the idle quality that determines where they should be. The engine lets you know where they should be. Counting the turns will get you in the ballpark after a rebuild, but the final adjustments are made with the engine at operating temperature idling, usually in gear if it's an automatic transmission.

Of course the needles need to be in good shape before hand, and has been said the orifices can be modified if need be to tailor the amount of mixture reaching the needles.

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Old 12-27-2019, 11:21 AM
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Put a vacuum gauge on the engine and adjust the idle mixture screws until you get maximum vacuum reading. Start with one screw and screw it in until the engine stumbles and then back it out in 1/4 turn increments until you get the max vacuum reading. Then do the other side. You may have to go back and forth both sides a couple of times to get it done. Put the gauge on manifold vacuum. If the car is an automatic you want it in gear when doing this. Set the timing first. If you do it and then mess with the timing then do it again.

As Sirrotica says the 1 3/4 to 2 turns out deal is just to get you started after rebuilding the carbs or engine or whatever.

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Old 12-27-2019, 11:23 PM
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Dick Boneske Dick Boneske is offline
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For your engine as you listed it above, I'd open the idle bypass restrictors to .052"(from the stock .046"). Idle tubes .038"(from about .034" stock). Idle adj. screw holes in the throttle body .073"(from about .070").

As Kenth said, the idle mixture screw taper will affect how many turns from seated gives smooth idle (max. vacuum). The stubby ones would require less turns out from seated.

If three turns out still gives you adequate spring pressure, and idle is good, I'd leave it as is.

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Old 01-19-2020, 06:43 PM
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Dick, I sent you a PM

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1966 GTO

1966 421-9.3-1 comp-Race Tec 23cc Pistons
1966 Tri-Power
1967 670 Heads
Pontiac "Highlift" TriPower Cam by SpeedPro
DUR 214 Int 224 Exh @.050 - 107 ICL
LIFT .445" Int .465" Exh
Tri-Y-Headers by Tribal Tubes w/ Goerlich Mufflers
1966 Muncie Wide Ratio 4-Speed
1968-72 Chevy 12 Bolt Rear End w/ 3.73 rear gears
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