Stumbling 390-2V . . Any suggestons?

I have a '69 Galaxie with a 390-2V that hesitates when you first press the accelerator pedal. After the stumble, it catches on a runs very strong and smooth, so something is just wrong in the initial tip-in of
the accelerator.
I have a nearly new Pony Carbs rebuilt Autolite 2100 in there . . have carfefully timed the car for a smooth fast idle and high vaccum. It doesn't seem like a mixture or choke problem, and since the idle is smooth I don't think it's a vaccum leak.
Does anyone have any ideas/experience in solving this?
Thanks.
Brian San Francisco
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First thing to check would be the accelerator pump. Do you know how?
Al
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No, not sure how to do that. Any tips?
Thanks.
B.C.
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snipped-for-privacy@gmail.com says...

The method you describe will usually lead to excessive advance. Use the timing marks on the harmonic balancer, get a strobe and do it right. Once you have it timed, then you could think about fiddling with the carb, but you apparently already have, so I don't know where that leaves you.
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snipped-for-privacy@gmail.com wrote:

Is there any 'popping' on decel? If so, too lean.
But, if that carb is the same as my 66 390 2V, I seem to recall the accel pump is adjustable. Could be wrong
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Backyard Mechanic wrote:

slotted for fine adjustment. The accelerator pump arm on some was slotted for more coarse adjustment. Smallblocks were pretty easy to adjust the pump stroke on because they just rev so quickly. FE motors were touchy about accelerator pump, vacuum advance, and initial timing settings because they reved up slower. Those engines would stumble on acceleration if the moon wasn't in the right phase or the temperature wasn't just right ;) This was a Ford thing on many engines through the 70s, but was most prevalent on the FEs. It can be fixed with some diligent tuning, at least for a little while. As a rule GM cars didn't suffer from this problem, but I remember some of the late 60s and early 70s HP and PI Ford motors that used the Rochester Quadrajet that still had stumbling problems. If you drive an old Ford with an FE motor, you learn how to wiggle your foot on takeoff :) How much depends on your tuning ability.
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snipped-for-privacy@gmail.com wrote:

accelerator pump a bit. First, set the timing to spec and verify thet the vacuum advance is working properly.
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