Classic/Antique Car Repair: Holley carb, holley carb, air screws

Question
I have a new Holley 4412 two barrel on a 350.The only problem I have is that when I get in it hard (in the shop or while moving) it hesitates then goes on. I tried these things,screwed out on the air screws a little, bigger jets , changed squirter (28 to 31)and no change. When I open the throttle with on hand and push down on the pump with the other, it don't hesitate at all. So then I loosened the pump spring until I had no more screw left. Didn't help. Any advise.

Answer
Carbs are VERY tricky... seams to me from  my experience that when a carb hesitates or stalls some thing internal is getting stuck. opening and closing the screws does nothing to alleviate this .
I would check your fuel supply and your filters..
Did you install new filters? did you use any Teflon tape?
This stuff ALWAYs gets into the jets.  
Start there then call the holley help line.
Good luck