need help fine tuning
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Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
need help fine tuning
i need help fine tuning my 428 when its cold in the mornings i have to give it half choke and rev it until it warms up but then it still will stall out and if you move the distributer to either side a little it stalls and what is the right method for adjusting the idle mixture screws on a holley 4160
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Idle mixture screws? That's easy. First, warm up the engine completely. Go for a drive and come back. Then, without turning it off, let it idle. Turn the mixture screw in completely, but dont put pressure on it. When it stops its in all the way. You'll notice the engine running rough. Then, slowly turn the screw out until the engine smooths out. No farther. Just enough that the engine runs as smooth as it is going to. If you have a vacuum gauge adjust it to maximum vacuum.
Then repeat on the other side.
Then repeat on the other side.
Post Fiend
Joined: Sep 2004
Posts: 5,231
Likes: 1
From: Near Fresno, California
You set the idle mixture with the engine warm - and the normal idle speed. When cold, the choke should not only close its butterfly, but also move a fast idle adjustment cam into your linkage. You adjust the screw or bolt on that cam for cold idle speed.
You have to press your gas peddle down and release it for this cam to fall into place before you start your truck.
Sometimes people disconnect this part of the linkage, or remove this cam; thinking it unnecessary.
You have to press your gas peddle down and release it for this cam to fall into place before you start your truck.
Sometimes people disconnect this part of the linkage, or remove this cam; thinking it unnecessary.
Thread Starter
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Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
why would moving the distributer a little bit cause the engine to just stall out in both directions it does this and what is a good pre set on the idle screws so i can get it to idle is it 1 1/2 turns out and i noticed my vacuum went from 20 down to 12 almost right away is it running to lean or to rich and what size main jets should i use.
Post Fiend
Joined: Sep 2004
Posts: 5,231
Likes: 1
From: Near Fresno, California
Your vacuum is low - do you have a aftermarket cam in your engine?
You were asking about cold starts - I assumed it ran good when warm - is that true? If not, you need to fix that problem first.
As to main jets, they are not an issue at an idle - whatever you have is enough, and the idle adjustment sets the amount of gas delivered into the airstream.
You were asking about cold starts - I assumed it ran good when warm - is that true? If not, you need to fix that problem first.
As to main jets, they are not an issue at an idle - whatever you have is enough, and the idle adjustment sets the amount of gas delivered into the airstream.
Elder User
Joined: Jan 2004
Posts: 867
Likes: 0
From: Eastern Pa
You still need to tell us if you have a healthy cam in it. if you do and you can't get it to idle down as low as you think it should, there is a fix recommended by some experts (HP books) by drilling a small hole in the primary butterflies right next to where the transition holes are in the bore of the carb. This lets a little more air through creating a situation where the fuel will now come out of the transition holes cause they sense the air rushing by.
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Fleet Owner
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