When sending the high-energy burst of electricity to the spark plugs, the magneto has to do so at the right split second—every time. That requires that the mag be timed internally and externally. Setting the internal timing requires that the mag be removed from the engine and opened up. It should be performed every 500 hours of operation. External timing is done with the mags on the engine and should be done every 100 hours or at the annual inspection.
Internal timing involves setting the point gap and “E-gap” (“E” is short for efficiency). The point gap is set first—and involves rotating the drive shaft to the position where the breaker points are opened as far as they will go. The gap is measured with a feeler gauge and adjusted to the distance called for by the manufacturer.