I got the new choke unit Sat. for the stock carb. I had completely rebuilt the carb earlier . Even with the new parts the carb was hard to start , and too rich . The new choke fits tight and stays where you set it. It must have been leaking too past the o-ring because the carb is now crisp and the plug looks good. I will still have to wait for final set -up since the motor is not broken in yet.