[rotorwrench]

I know nothing about this system or application but I've got a long history with all sorts of aircraft, industrial, and motorcycle magnetos. Assuming the magneto is timed internally and makes a spark to each plug in turn, I would be wondering if this mag is fixed for timing during road operation or does it have any form of spark control adjustment for starting and load? Most magnetos are not advance or retard adjustable so they are fixed for running at operating rpm. They will usually have an impulse coupling that delays the spark for starting and then kicks out to full advance after the engine is running by way of flyweights. Other starting aids are also used such as a starting vibrator circuit that provides a shower of sparks but works through a separate set of retarded timing breaker points.

Magnetos will give a spark at low rpm but it is weak until the rpm builds a little. It is still strong enough to light off a good fuel mixture though. If there is no way to retard the spark then the engine can kick back and damage a starter or some poor souls arm.

Internal timing of a magneto will always require the breaker point firing position to be synchronised with the rotating magnets E-gap. This is the point where the magnetic field is at it's stongest in the laminated core of the coil. When the magnet is in the E-gap position, a person can feel it as the magnet is rotated by hand. It wants to stick at this point like a magnet sticks to a piece of iron or steel. As it rotates past the E-gap, the magnetic field collapses which induces the coil to step up the voltage to the primary side and make a spark as long as the breaker points open at the right time.