Check for vacuum leaks around base of carburetor. Spray some carburetor cleaner or starter fluid around the base of the carburetor while the engine is running. If the idle speed increases, you have a leak. You may have a plugged jet or passage inside the carburetor. The mixture may be adjusted too lean. The carburetor float may be set too low or is binding (not enough fuel in bowl).
Probably best to just take the carburetor off, clean, blow out all jets and passages, and replace all gaskets. Not that hard to do.
John