Ok I have had this problem get a small screw driver first off, then go on e-bay buy carb kits and rebuild them 280 mains should be fine. for some reason even if I clean the carbs good it still runs funny so buy the kits and rebuild them should solve your problem. its not getting enough gas that why when you choke it it reves high cuz you are cutting off the air . also check your fuel valve make sure you have no clogs if there is a filter change it or get rid of it. hope that helps