[wilf leek]

Clois - if the bog is immediately as you put your foot down, then probably the accelerator pump needs a bigger (or smaller?) shot - there are different holes in the linkage arm on the edelbrock carb you can choose from.

If it's after that, and at WOT, then maybe the secondary jets need to be looked at. The step up valve springs could also be the cause, but they should not affect WOT.
A bit more detail, such as at what revs this does/ does not happen etc could help the diagnosis. Is this a quick transient effect, or does it persist for a few seconds?
IMHO a session on the dyno is the best way to sort carb problems out. You can't fool an air-fuel ratio meter!

I do find that on my own car, with Edelbrock 800cfm carb, it does not particularly like WOT below 3000rpm in the higher gears - revs pick up too quick in the lower gears to make any difference!