Holley Carb Tuning Help

H

hassler

Member

Aug 18, 2025

34

10

18

St. Louis

Oct 25, 2025

#1

• Oct 25, 2025

• #1

Got a Holley 4150 on my 91 carb swap. Built 302 motor, still working out the kinks.

I didn’t setup the drivetrain or carb. Nor do I think it was set up or tuned correctly.

Currently to get the car to start, I’ve gotta give the 2 idle mixture screws about 4-5 turns out from baseline. This works and car runs fine but reading that it should only need about 1.5-2.5 turns out. The guy who set this up before I guess has it bypassing the idle circuit. Any advice here?

do I reset main idle screw? Add air with secondary idle screw, then do idle mixture screws? Set idle speed

 

Blackhawkxx

Advanced Member

Mar 3, 2023

460

458

73

Oct 25, 2025

#2

• Oct 25, 2025

• #2

1. Check that the timing is correct.
2. On warm engine, set base idle.
3. With vacuum gauge connected, turn each idle air screw to get the highest vacuum. Take your time with this.
4. Or maybe this should be #1, if the car truly does start and run great, don't touch it.

 

Reactions: RaggedGT

H

hassler

Member

Aug 18, 2025

34

10

18

St. Louis

Oct 25, 2025

#3

• Oct 25, 2025

• #3

Blackhawkxx said:

1. Check that the timing is correct.
2. On warm engine, set base idle.
3. With vacuum gauge connected, turn each idle air screw to get the highest vacuum. Take your time with this.
4. Or maybe this should be #1, if the car truly does start and run great, don't touch it.

Click to expand...

I’m familiar with carbs and tuned it today, just never down this Holley particularly. Just read that it should only take 1.5-2.5 turns on the mixture screws. And that 4-5 turns out wasn’t right. Which that sounds right to me but I think to achieve that will take a whole tune from total zero

 

General karthief

wonder how much it would cost to ship you a pair

5 Year Member

Aug 25, 2016

27,866

10,540

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polk county florida

Oct 26, 2025

#4

• Oct 26, 2025

• #4

The 1.5-2.5 turns is a starting point.
You got it this way?
Check float level
Check throttle blade adjustment
Make sure squirters are squirting.

 

H

hassler

Member

Aug 18, 2025

34

10

18

St. Louis

Oct 28, 2025

#5

• Oct 28, 2025

• #5

General karthief said:

The 1.5-2.5 turns is a starting point.
You got it this way?
Check float level
Check throttle blade adjustment
Make sure squirters are squirting.

Click to expand...

Yeah I got it this way. New built 302 with roller cam, afr heads, long tubes etc. Mechanic had a lien on it and sold it for the $ he had in the drivetrain so way under value. However I’m realizing he took plenty of short cuts to get the car running and sold. Still can’t complain for the price I got it. Once I’ve got this carb right I should have most everything fixed

 

Reactions: gkomo

R

Rcdgl

5 Year Member

Feb 19, 2018

313

168

63

Oct 28, 2025

#6

• Oct 28, 2025

• #6

Check for vacuum leaks, then check the idle slot vs the throttle plates. Make sure you dont have a gas leak from the secondary somewhere.

 

Reactions: General karthief

85GTStangGuy

5 Year Member

May 19, 2021

998

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Jax, Florida

Oct 29, 2025

#7

• Oct 29, 2025

• #7

A carb rebuild may not be a bad idea either....