I have a push mower Cub Cadet CC500 running rough then I couldn't get it to start at all, Took it to a guy to get worked on and he clean the carb and said everything was ok, Today when I went to use it the motor still seemed to run fast then slow down some then pick up speed again after about 10 minutes the motor would almost shut off then start right back up for a few seconds then keep repeating itself, Then all of a sudden the motor stayed running again but it would run fast then slow down alittle as before, Any clues what to check for?