It seems to me that most probably the flywheel key has sheered, thus putting the ignition timing out. You need to remove the flywheel and replace the small alloy key. You must ensure that it is replaced with a genuine alloy key and definitely not a steel one. Additionally, when you try to start It , you should pull on the rope very slowly until you feel the compression, and then pull it past the top dead centre point, so that you are commencing your start pull on the down stroke of the piston .
John, November 2009
