Carburetor issue

The float level may be too high causing a over rich condition, power valve may be leaking as well, high fuel pressure can also be a problem. i would find a mechanic comfortable with working on carburetors, this is some what of a lost art now days, so call around and see if there is someone close to you that is happy to look at the carburetor.

I wonder if this vehicle is in an area with ethanol in the fuel? If so that carburetor has parts that do not like ethanol. As MHP says you need someone who knows carburetors. A good starting point would be a rebuild of the carburetor and a good cleaning. Then start tuning it in.