Carburetors can often be cleaned successfully with a Seafoam Treatment. This link to the video will show you how.
I did it to my generator last year after we bought the RV. It had been sitting unused for quite a while and was running very rough. Now that we have it running well, I make sure to run it under load for at least two hours each month.
After cleaning, you should probably adjust the mixture.The mixture adjustment is the "altitude" screw on the side of the carburetor. With the engine running under load, turn the screw counter clockwise about a 1/4 to 1/2 turn. The engine should start to run a bit rougher. Hold a white rag or paper towel about 2" away from the exhaust pipe. It should have some black soot showing. Turn the screw clockwise 1/8 turn. It should sound a little smoother. Hold the towel to the exhaust again and see if there is still soot coming from the exhaust. Keep adjusting 1/8 turn at a time until you no longer see soot on the towel and stop. You can try a slight counter clockwise adjustment and see if the soot reappears. The best adjustment is just at the point where the soot stops. Any further is too lean.