Most likely in stock configuration, your clogged carbs were barely able to keep up with flow. Add tiny bit extra and they can't keep up. You need to take apart carbs down to individual jets removed from emulsion tube. Each and every bleed hole in jets and emulsion tube needs to be physically flossed out guitar wire of matching diameter. You'll find that spits out little plastic plug on inside. I also drip dye down centre of jet & emulsion-tube to verify each bleed-hole "bleeds" properly (Kool-aid or fruit-punch mix works well). Also clean out idle and transfer ports in carb venturi with wire. Then soda-blast every hole and circuit to clean out scrapings.
