Newly rebuilt Holley 4000 on a 312 YBlock in a TBird. All works well except there is a terrible gap/sputter when coming off idle. At a stop sign when I apply pressure to the gas pedal slowly as normal, there is a terrible hesitation. If I apply gas more quickly it goes right through it without trouble. It even happens when getting back on the gas after slowing a little for a turn etc..

Any thoughts?

Thanks very much