I use Q-Tips (a lot of them) after total disassembly of each carb. My favorite high is lacquer thinner: having a lit candle nearby (BEFORE you start using it, not AFTER the fumes build up) will keep the fumes at bay by burning them off in the air as they appear (a trick I learned from someone who used to paint model trains for a living). Acetone almost works as well, mineral spirits not so much. The green CRC brake cleaner spray is also excellent, but expensive to use, for removing thick layers of the gunk in nooks and crannies. Gently scrub the floats with a brass toothbrush (like in the detailing kits for cars, at auto parts stores) to remove buildup on them. Don't soak the plastic floats in acetone or lacquer thinner, but the brass ones are OK for that.
Be sure to clear the air passage between the air horn (little brass hole) and the emulsifier tube (aka mainjet holder) with a mechanic's wire. A little corrosion in there makes for a real rich mixture later.