The fly wheel key is located under the pull rope, take every thing off until you get to the flywheel, take the nut off (if it's tough to get off, put a clean rope in the spark plug hole to jam the motor and you can remove the nut)
After you get the nut off you should see the flywheel key way, it should make a perfect square, even it's sheared a little bit, that can throw timing off.