Sounds like the accelerator pump circuit is not working. Either a ruptured rump diaphgram or the passage from the pump to the metering block has some crud in it.I got it idling at 1000 rpm, If I put the gas pedal to the floor, She pretty well dies out then kinda comes back to life then revs. I expect foot to the floor rpms to sky rocket. I hace a 770cfm holley truck avenger carb, edelbrock performer rpm air gap intake. I had the truck insured 3 months, it ran great. Then I parked it and while it was parked I swaped on the new intake, Marked the timing but it could be out a tad. I have played with air fuel mixture as well. I cant figure out why its doing this.
EDIT: I dont think its a vacuum leak, I got 21 psi at idle.