Remove the screen that covers the flywheel.That will expose the timing marks that are on the flywheel shroud. The flywheel is marked with the letters DC near one of the flywheel fins. the fin is further identified by an X mark cast on the end of the fin. Turn the engine over until edge of the marked fin on the flywheel is on line with the mark on the vertical line of the shroud. At this point the key way for mounting the flywheel is also on top. The magneto should now be fitted to the engine so the X marked tooth of the magneto gear is visible through the lower half of the inspection hole.
If the magneto is properly timed the impulse coupling will snap when the DC X marked fin lines up with the center line of the number 1 and 3 cylinder as marked on the flywheel shroud.