I have an ms210c that hasn't had a problem until now all of a sudden it wont fire at all when choked. Use to start like a normal saw- usually 4 pulls cold and choked to get a fire. Then a couple more pulls to start it. Now I can pull it choked until I need a rest and it never fires. Just wondering if there are any known fixes or things I can check before pulling it apart. I've never worked on a stihl so it could take me a while if I have to open it up.