Please explain Idle adjustment screws - JeepForum.com

 
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post #1 of 4 Old 03-05-2014, 07:05 PM Thread Starter
CJWeaver
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Please explain Idle adjustment screws

I have a 1982 model 4.2L with a stock Carter 2bbl BBD Carburetor. One of the guys at work offered to see if they can fix my rich idle by adjusting the idle mixture screws on the front of my carb. When I started reading for instructions I found they were contradictory. Some say that turning the idle screws in (clockwise) makes them leaner while others say that backing them out (counterclockwise) is what makes them leaner. Can somebody explain how they really work and the easiest way to set them close?

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post #2 of 4 Old 03-05-2014, 07:19 PM Thread Starter
CJWeaver
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I am sorry I have no idea why the system duplicated my question.
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post #3 of 4 Old 03-06-2014, 03:31 AM
John Strenk
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Turning them in makes them "Leaner"

Don't read any further unless you want to know the rest of the story.
You can stop right here and know all you need to know.




Since the fuel coming out of them is already mixed properly, they act like teeny tiny throttles.

It gets really complicated when you factor in the transfer ports. When the throttle is closed, the transfer ports lets more air into the fuel idle circuit making it leaner. When the throttle passes the transfer slot, it' lets out more fuel making the mixture richer.

But it's just easier to think of idle screws controlling the idle mixtures so lean-in rich-out


You can see the taper on the idle screws and turning them in will limit the amount of mixture coming into the engine.




here is a good picture of how the transfer ports work:
It's for a progressive Weber carb but the theory is the same.
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post #4 of 4 Old 03-06-2014, 04:20 AM
John Strenk
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Quote:
Originally Posted by CJWeaver View Post
I am sorry I have no idea why the system duplicated my question.

Oh Never mind, I see this was a Duplicate....
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