After 4 years it's probably time to take it apart. First make sure that fuel line is not clogged and enough gas gets to carburetor. If flow is good, cleaning carb would be the next thing I would try. Also, your air filter is clean, right? Get some good spray carb cleaner (make sure it has toluene, the "environmental" stuff sucks). Spray the outside before you take it off. The carb is not that hard to take apart, just study it as you go and don't get rough with it. You will need a small screwdriver, like a jewelry size to take out the jets. Clean the passages with small copper wire. Twisted strand electric wire sometimes works on the really small passages. Use the carb cleaner on parts that have any varnish on them. Some of the passages may be recessed and hard to see, so a flashlight may help. Get a good place to work so you don't lose any small parts, and don't get any carb cleaner in your eyes. Good luck.