I'm working on the carburetor for a 4hp engine. The carburetor has a check ball in the main nozzle. The ball keeps sticking. I get it free so you can hear it rattle when you shake the carb. The engine runs and when I shut it off the ball is stuck again and it won't start. Pull the carburetor and free up the ball and it runs again. I have soaked the carburator overnight and the ball is still not staying free. Has anybody had any sucess removing and cleaning that foot valve? Any tricks for polising the check ball?