Holley 750 "stumbles" on WOT

Lift&Move said

Hello All,
I purchased a nice used carb from a fella a while back.
It was on his 68 RR, 440 auto.
The facts are these :
Worked perfectly when new, but over time when stomping it to the floor from a dead stop, it would hesitate for about 1 or 2 seconds then WAHHHHHH
He replaced it with an identical new carb and his problem was solved.
I have a new kit for it, but would like to know the source of this particular symptom for future reference.
Thanks

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Most likely when you stomp it the vacuum drops dramatically in the intake manifold causing the fuel to return to a liquid state then as it hits the floor and walls takes time (longer) to get to the cylinders as fuel on the walls and floor travel slower than fuel entrained in the airstream.

I would suspect it is a pump shot issue so start there. I would also check the IFR and IAB sizes to make sure its rich enough on the Tslot. The Tslot fuel is quicker to respond to rapid opening of the throttle blades. You can actually make the Tslot circuit rich enough so as to not need the pumpshot circuit but that creates other problems.