Is the air gap between the magneto and the flywheel correctly set?
Take off the at cover and loosen the two small bolts that fix the magneto to the engine casing.
Turn the flywheel so that the magnets are directly opposite the magneto.
Slide a business card between the flywheel and the magneto. (The card is roughly the same thickness as the airgap)
Tighten the bolts on the magneto replace the starter and spin it over. It may start.