If it's a Walbro carb, take off the choke plate, slowly pull the brass rod out with the carb facing down. A small ball and spring should fall out of one end. If not, hook it out with a piece of wire. reassemble and tighten the choke plate quite tight. You might want to slide a spring on so it's between the carb body and the choke arm to stop vibration from wearing the choke plate.