I could use some help with a b&s carburetor. Model 259707. My neighbor brought this over to get repaired. When cold the engine starts fine and runs for about 3-5 min. and then it starts to flood out. It eventually dies. The carb has been pulled and cleaned twice. The bowl float is plastic with no apparent holes. The needle seat has the Viton on the end. I screw the jet all the way in while it is running with no results. I am puzzled. Help me guys!