holley 750 carb hiccup?

hello all, odd one here, had like a miss, would clear on higher rpm but still not pull clean, it was like several leads were breaking down and coming in at the same time or you losing ign for a second then getting back but know not ign as not misfiring, i swapped the leads anyway wondering any suggestions on carb, its a freshly rebuilt holley 750 vac sec, igh is new msd streetfire,new elec dizzy and new coil, wiring is 100% as i rewired whole car, i have a soot deposit around top of carb / butterfly, hoping its not a valve blowing back but the carb popping back thro, cheers in advance, nathan.ooh, its a 440 manual.