Try a vibrator?
A few years ago I bought a hydrostatic cleaning gizmo from Harbor Freight. Cost was about $45-$50. I totally strip the carbs down, clean everything with carb cleaner, blow them dry with a pressure hose, then throw them into the hydrostatic cleaner that's filled with water. I was amazed at the stuff that came vibrating out of all those little holes. I've even vibrated the parts with solvent in the machine (NOT recommended by the maker). They seem to work a lot better without taking them off and trying to clean them again, then repeat again and again.