Help With Carter Afb

BOSSC351

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Founding Member
Aug 1, 1998
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De Kalb, TX
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I am having a hell of a time with this 750 Carter AFB on my 351 Cleveland. I have changed rods, jets, vacuum springs, and accelerator pump setting and still have a terrible hesitation or stumble at about 2000 rpm when accelerating or going to wot. It will basically die then take off like a rocket. I also changed advance springs and bushings in my distributor with no luck.
 
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tos

SN Certified Technician
Apr 27, 2001
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Cincinnati Ohio
Is this a new carb? does it stumble immediately when you stomp on it or is it happening just when it reaches 2000 rpm?
Is it only during quick throttle movements? If its immediate then I would revisit your accelerator pump adjustment. I'd say about .010 or less gap between your pump arm and the adjuster. Its possible too that if it were misadjusted and you went wot that it could have damaged the pump diaphragm (generally would have to be way off adjustment but is possible).
 

BOSSC351

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Founding Member
Aug 1, 1998
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De Kalb, TX
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It was new back in 97 when I got it but sat in the box till 2013 when I completed the engine swap. The stumble happens when I stomp it at about 2000 rpms. It stumbles and cuts completely out then the engine takes off. Also when slightly increasing the throttle a slight stumble can be felt then all is good. I have verified the pump squirts. I have tried all three holes in the pump. I thought going to the strongest vacuum spring helped a bit but it is back to square one.
 

7991LXnSHO

Mustang Master
Sep 1, 2010
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Kearney, NE
I think you are on the right track with timing advance curve and the accelerator pump first. (I usually do Holley or GM carbs, so some of this is general advice.) If the pump circuits and nozzles are clean, the nozzles are big enough, and the rubber parts (plunger on AFB?) are good, adjustment is all that is left. The power valve in a Holley, or the power enrichment circuits in any carb might be problem.

Brainstorming, how tight is the spring for the secondary flap? If it is flopping open too soon, it can bog. Try adjusting that tighter. The worst thing that will happen is your mileage will increase. After that, low float levels are a more remote possibility. There is not much else left.