I have a 67 gmc 1/2 ton.It has a 305 v8 and i believe the proper 2 barrel(2gc) carb for that engine.My problem is that it has a hesitation when you mash the throttle.I rebuilt the carb myself.The accelerator pump appears to be working properly.When driving slow and you mash the throttle it hesitates then takes off or stalls.It seems that maybe its not getting enough fuel at that time.If i close the choke plate some or hold my hand over the carb it will rev up everytime but if I don't restrict the air it will bog out. Does the power valve take affect in this kind of situation? It seems to have good vacuum when idling.It idles good and drives good but even if you quickly step on it,and even half throttle,it hesitates.Its got me stumped.Any info would be greatly appreciated. By the way ,not that it matters,it has a turbo350 tranny. Thanks.