What KZ said.
Test the water: the bottom of the carb bowl will have a drain. My Mikuni carbs on my '82 GS550 had just a bolt, take the bolt out and you're left with a hole for the fuel to come out with. My current bike has a nipple you can put a tube on then a screw to let the fuel come out. Either way, drain the bowls into a dry and look at what comes out. If you see some separating in the liquid, you have water. My kawi once got at least a quart or two of water in it, and the stuff that came out looked like water, smelled like gas, and you could see something like putting water on a greasy pan. The bike didn't want to start at all. I took my carbs apart for cleaning, they were filthy. You might be able to just put some cleaner into the fuel and not have to take the carbs apart. You can get some at auto parts stores. If that doesn't help, you'll need to take the carbs apart and fully clean them. Then synch them.
It's possible that the idle mixture screws loose their adjustment after a while. Do what ZXLNT said to get at them. I think yours might be on top of the carb, not on the bottom, though. My Mikunis off my Suzuki had them on top, and the Keihins on my Kawi have them on the bottom. The ones on top are easier to get at. What you want to do is turn them so you have the highest idle. A 1/4 turn might affect the idle by 50 rpm or so (if you're close to what it should be), and it can seem unstable, but if you stare at it long enough and listen carefully enough you can tell if it's going up or down when you turn it a certain direction. Play with it until you have the highest idle, as that will be your most stable idle.