My Express-SR won't start unless I stick my thumb in the throat to choke it. It will start then and if I keep it running by this method until it warms up it will run OK. I've had the carb off and cleaned it, then cleaned it again to be sure. the air screw is set at 1 3/4 turns and I've tried turning it in and out. I cleaned the choke control box as well as I can tell. It passes fluid and air OK. Blew everything out with compressed air when I cleaned them. I still supect the control box may be faulty. Advise would be welcome. Does anyone know if parts are available?