Is this a 2 stroke...and if so check if it needs a decoke...carbon build up in the exhaust port and muffler are the most common problems with 2 strokes.
Easy to fix...remove the header pipe and carefully scrape any build up out...a blow torch can be used to burn the carbon out too. Same with the muffler...which usually have a removable baffle that can be burned free of carbon with the blow torch...or use a wire brush to get rid of it.
Good luck and if its not a 2 stroke disregard all of the above.
Oh wow didnt see the date...bit late with this advice...hahahaha