How bad are they? I got a bike running once that I didn't think would ever run. The guy had left his bike sitting out in the weather for 10 years, and the gas had dried up and HARDENED inside the carbs. It took some creativity, but I got it out. I had to take a torch and heat up the carb bodies enough to soften up the crap inside to get it all out.
Generally though, get yourself a gallon can of Chem Dip. This stuff works great. Strip the carbs down, take all the plastic and rubber parts out (this stuff WILL make mush out of rubber) and drop them in the Chem Dip. Let them sit for a day or two in there and you should be able to clean them up nicely.