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Old 09-27-2002, 09:41 PM   #1 (permalink)
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Tuning Carter AVS/AFB

Any advice on tuning a Carter avs/afb? There's 3 knobs..2 on the base of the carb, and one between those 2 above them..what does the middle tuner do exactly? what is the strategy here?
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Old 09-27-2002, 11:45 PM   #2 (permalink)
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Tuning Carter AVS/AFB

If I'm not mistaken, you can probably use the Edelbrock website to get tuning instructions that will work on Carter/AFB.

www.edelbrock.com
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Old 09-28-2002, 01:59 AM   #3 (permalink)
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Tuning Carter AVS/AFB

AVS: Air valve secondary
AFB: Aluminum Four Barrel

Ok, that said, what's the difference? They can be mistaken. Let's have a look at your carb and see which you have. The AVS has a spring operated secondary flab, no boosters, a 3-step metering rod.
The AFB has a counter-weighted secondary flap, boosters, and a 2 step metering rod.

They both have two idle mixture screws on the front. Is the third one considerably different looking than the other two? If so I think you're just looking at a plug that has a screwdriver slot in it for vacuum accessories off the front.

Is this a new carb? If so it's probably the Edelbrock version.

Hope this helps.
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Old 09-28-2002, 03:07 AM   #4 (permalink)
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Tuning Carter AVS/AFB

No, this is a genuine 750 AVS off a 1967/68 Mopar 440. The third one is ABOVE and between the idle mixture screws, forming a triangle.. the 2 idle screws are in the normal position on the basleplate, but the third "?" screw is a mystery it has a spring like the idle one, but screws into the carb, and seems to affect idle quality/vaccuum/characteristics like the other _2_.. strange.
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Old 09-28-2002, 01:57 PM   #5 (permalink)
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Tuning Carter AVS/AFB

Well son of a gun. There it was. I went back to my AVS diagrams and sure enough in 68 and 69 they added the third mixture screw.

My suspicion is that it must be more of a "master" control that feeds the other two slots. I can see in my pics of AVS that a boss was there in the earlier carbs that just didn't have a screw in it.

I would highly suggest posting the question on the Mopar boards since there's going to be an AVS guru hanging around...

Keep us posted on what you find.
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Old 09-28-2002, 02:18 PM   #6 (permalink)
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Tuning Carter AVS/AFB

sure thing!.. yeah..wierd ****.. heh The mopar boy's carbs rock..just hard as f#%! to tune Very nice carb though.
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Old 09-28-2002, 02:52 PM   #7 (permalink)
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Tuning Carter AVS/AFB

I could be wrong on this but I think the middle screw is for idle speed. I seem to remember tuning up an old Pontiac that had Carter carb with what you descibed and thats what the middle screw was for.


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Old 09-28-2002, 02:53 PM   #8 (permalink)
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Tuning Carter AVS/AFB

I wonder if that third screw adjusts the mixture on the transfer slot, when you're at part throttle and halfway in between the idle circuit and the main circuit. I REALLY wish my Edelbrock had an adjustment for that, because it's a very lean spot. I've compensated for it with a little richer idle mixture, but I'd still rather have the adjustment necessary to fix it. Oh well, heh.
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Old 09-28-2002, 04:38 PM   #9 (permalink)
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Tuning Carter AVS/AFB

Yes, I think Motorhead is closer..it is NOT idle screw.. it affects idle VAC though..
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