Yep - its called : " Tip-in Sag" & Some Carter AFB (Usually The Emissions/economy jetted ones & some batches of edelbrocks are know for that on certain engines - changing the accelerator pump thinking its old/shot won't fix it (in a normal sense)
I've got the fix-it article around somewhere, but it was to do from memory too lean idle transition circuit , try raising the float level say 1/16th-1/8th inch , try backing out the 2 idle mixture screws 1st & if that helps slightly you'll have to delve deeper I'm not sue if a pair of slightly richer primary mettering needles was a cure (& check the obvious for cracked/split vacuum hoses giving mild vacuum leak.

Probably smartest thing to do is email or phone edelbrock techline & ask them ; I'm not sure if its them or another firm that brought out the Carter AVS again , in a modern revamp,but that gave similar effects on a a certain dodge 340ci & 1 year-model chev running it.

Not sure if AU's Hume Performance know enough to help,but if you get stuck, in my black book I've got a USA carb rebuilder contact whos more likely to have a cure at his fingertips (he's on Ebay too,so I'll duck back in later & leave his contact name on here,if you want )


This Problem 1st went public When Hot Rod Magazines Gray Bakersville Model A Hotrod was given a revamp & had an AFB/Edelbrock 500 or 600 fitted to its 283 or 327 & while jumping the mpg up 3-4mph with good response it had that annoying sage as you'd be cruising at 20mph & they're be nothing for a 2nd or 2 .
If You've got a carter competition 500cfm don't forget to give the carb number on the drivers side front right carb mounting boss stamped vertically on its foot facing front eg 6229S

your edelbrock will have a similar identifier,if you've got the shipping box & instructions if new, go from that,
With 80 looked into this topic & no ones stepped in i guess we're truely into the EFI age.
Or no-one knows anything beyond eyeballing entertainment...
Goodluck & leave a message back,if more info etc needed, cheers