Holley/Demon Carb stumble
Every time you go smaller on the MAB you make the booster come on later. So you effectively make the transition take longer, as in transition from the T slots to the booster.
You are trying to correct a very small top end rich condition by squeezing the MAB down and you ain't there yet. That's what I'm saying to you. You ain't that close.
I forget what you have for emulsion but post that up if you know what it is. You probably have too much and that will cause fuel to slug in the main well. It's kinda like when you turn on a hose for the first time and it pushes out some air and then water and it spits and sputters until you get solid water. That's what happens when you get too much emulsion. I can't remember what blocks you have.
Again, you are way out over the skis trying to pinch off the MAB and following the O2 sensor. I believe the plug long before a sensor and that thing is rich.