Check you valve clearances again. Just to be sure that a lock nut has not come loose etc.
Id say with your fuel cleaning, its been ok and now its not again. Id be getting into that carb. Can of carb cleaner, compressed air and squeaky clean it. Lay it all out on a nice clean old sheet. Continually chean your hands.
(you might be able to get a new one on eBay Ex USA for a good price too)
