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Newest update to carburetor stumble

Dead lean for 3 seconds?

What are you running for initial/total timing?

Do you have a video?
2200 - 2500 rpms

And exactly how are you getting into the throttle for the stumble to present? Are you stabbing the throttle to the floor and it stumbles, or are you slightly squeezing or rolling into the throttle to accelerate a little and it hesitates?
I know you probably heard this before but are you absolutely certain the Float levels are correct? Too low would cause hesitation.

If you cruise at 3000 rpm and stab the throttle, does it still stumble?
4 different carbs and no change indicates to me you may have a problem with something else.
I'm afraid I'm going to have to agree with this.

At this point perhaps you can borrow someones known good intake, and possibly a known good distributor. Never assume that just because its new that it can't be the problem.
I fought for days with a new 440+6 conversion a few(?) years back only to finally realize that the brand new intake, from MoPar, itself was porous. Warranty covered it, swapped it, and it ran perfectly from there on.
Cam timing would be my only other 'guess'.

I wish you well
Actually five different carbs

Intake Manifold also was mentioned in the first thread
Fred the GTX with his rather mild 440 absolutely misbehaves on the typical gas station (alcohol added) gas;
you get some "straight" 93 octane though and he literally straightens right up within a few miles.
It's actually quite surprising the difference it makes...
I wish I was closer to you I would go for ride and try to help figuring out
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