That's what we don't know. Jpar says he can see fuel standing off when he mashes on the throttle. I've posted earlier you usually don't see that on stuff with a plenum. You see it with stack injection and Individual Runner carb stuff.
And usually, you see the stand off at idle or very low engine speeds. If you see a stack injected engine with a lot of overlap you can see a mist form over the stacks at idle. It's quite a show sometimes. They can mist, or they can look like little balls being juggled around.
I think if Jpar can get the bog out, he may eliminate the stand off at the same time.
Air does incredible things when it's pissed off. It can flow one direction in one part of a port, and flow the opposite direction in another part of the very same port. I suspect that something similar is happening here. That bog is doing something to upset or exacerbate whatever reversion there is happening under the carbs.
It will be interesting to see how it all washes out.