Two things to check first. The very first thing is to make sure the pull switch is in the correct position. I have one that you pull the switch out to start and another that I have to push it in to start. They both look alike. If you don't know how to check the switch just remove the wire on the side of the magneto. The switch to a magneto just shorts it out to the frame.
The other first would be to clean the points. Many times the points have a film form that keep them from making a spark.
Those can be done without removing the magneto.