I'd bet a good carb cleaning and you are set. Probably get a kit online and to your door in a few days.
Take it apart, soak it for a day or two, clean it up, put it back in and I bet this will get you on the right track. Adjust it (tune) as needed of course.
(I assume you did all the basic stuff like looking at the plugs, adjusting carb, spraying cleaner in there, etc..)
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