Not sure about yours, but the keihin carbs on my '85 nighthawk had three circuits like Pvster said (4 if you include the choke circuit). If you're mechanically inclined I'd recommend taking it apart and cleaning. I haven't tried the boiling method, but I do know that a high-pound test fishing line (nylon) is great for cleaning all the little holes and ports - just poke it into the holes and see if anything gets pushed out. NEVER use anything that could scratch the body (guitar wire, etc).
If you're less technical/want to try a "quick" fix, shut off the gas valve, run the carbs out of gas, detach the gas hose then fill the carbs (through the hose) with Seafoam. Probably want to leave it overnight if you do this.
My guess though is that you're probably better with disassembly since an occasional problem would indicate that its probably something other than just gummed up gas (maybe a piece of rust?).