Get a gasket set for the carb and a spray can of carb cleaner. I normally use B-12 that comes with a straw that you stick in the nozzle (good for spraying into the little holes). Take the carb apart then clean it really good. I mean use the whole can of cleaner. What I do is spray the parts over a coffee can so that some of cleaner is captured then i drop every thing in there for a while just to make sure. The problem is that the ethanol destabilizes the gasoline after about 3 months, leaving a nice gummy residue in the carb.
I was told to run premium in the small engines because it has less ethanol or to run a fuel stabilizer in it.