Carb seems to have tendency to cough back if opened quickly or if power is slowly applied at higherspeeds. The engine may suddenly give a big burp or cough .
Its an 870 avenger on 454BB with Performer Rpm manifold, oval port GMP parts heads,MSD6al with hei distributor.Cmp Cams Xe 274 H cam.Compression approx 11.00(LS6 shortblock)18 degrees initial timing (no vacuum advance)
I have changed the power valve to an 8.5 from what was in the carb originally.This really helped driveability to eliminate big flat spot in slow speed part throttle tip in.Is primary side possibly jetted too lean?It already has #78's.Suggestions?

How much vacume do you have?Power valvel should me half that.Have you checked float level?Air mixture?

Jetting ,I need help there though graemlins/clonk.gif

I have a similar problem with my 650 Holley (Q-Jet replacement) on my 305 (will be replaced once my new engine project gets underway) that coughs through the carb if I try to take off from a stop. Especially when cold. When hot, it tries to bog.