Energy Transfer Magneto

- Hoyt McKagen

Energy Transfer Magneto is easily made from standard alternator as used on most earlier model Hondas of all sizes. Alternator is a six pole, split coil arrangement with a perma-magnet button rotor. There are differences in the design among models and year, but all are suitable for conversion.

Many of these will swap between motors, but since individual units are wound respective to demands of the number of spark coils, the number of cylinders/coils should be the same.
ETM is wired so each coil primary has a stator coil, set of points and capacitor. Each of these components has two connections, one of them usually grounded as mounted. To complete ETM wiring, any remaining ground connections are made, and components are connected together at the other ends, that best being done by one primary lead from each stator coil pathed thru points, cap and coil in their usual mounted positions. The primary may have sockets spliced into it at various places to facilitate connections. This same lead can be extended to the kill switch; for twins and multis that can operate by connecting the involved stator coils together. Usually spark coils, points and caps can all be stock components as used with the original cycle, and mix and match is often successful. I've got a CB360 barking with Yam coils from a CDI model Triple coils and in general, CDI coils often give slightly better results.
Alternator coils are in two sets distinguished by wire size and number of turns. As shown, there are four lighting and two iggie coils. On the stator, the iggie coils are opposite each other and so are pairs of lighting coils. The two lighter-gauge iggie coils are wired in series and are connected to brown or pink common lead, along with one end of the lighting set.

On single-coil setups (thumpers and 360 twins), the iggie coils can be used as wired, with the brown lead grounded and the yellow lead from iggie coils used for the primary lead. On twin-coil setups (180 twins and multis) the iggie coils must be separated at one end from common and an extra primary lead brought out from the disconnected end. Somewhere between these two coils their connection must be isolated, spliced to a wire and lug, and grounded to a stator mounting bolt.
Battery/coil systems flow current thru coil when points are closed, building magnetic field around primary to saturation. When points open, current stops flowing and magnetic field collapses. Energy contained in field excites voltage flow in both coils, generating spark voltage in secondary. Primary coil and capacitor form a resonant circuit that also feeds energy into secondary coil, prolonging spark and probably accounting for spark 'ringing'. Battery/coil system thus has two instantaneous sources powering the spark.
ET magneto operates in essentially the same way except for the stator coil subbing for the battery, hence the similarity in the wiring. However, the magneto has an extra instantaneous source: there is energy stored in the magnetic field at the rotor/stator interface that is also available to the spark as the points open. A battery cannot supply that kind of pulse! But stator coil also can't give continuous power, so points must open and spark be produced when it's giving its best. Usually, the magnetic pulse isn't wide enough to give you the full original range of advance, so it may be limited to about ten degrees or so (by brazing blobs onto the advancer stops) or advance simply be done away with. I do the latter and find it has no effect on performance nor if well tuned are they tougher to fire up.
Usually the desired pulse isn't where keyway places the stator. Often when setting these up a specific procedure is helpful: Wire and connect the ET setup and lock out or limit the advance mechanism. For timing purposes, temporarily lock in full advance. It's helpful to loosen the valve adjuster screws, to keep spring pressure from moving the motor; indeed one can also set these so the motor will stay in the desired place. Remove the rotor and replace it on key, loosely secured. Time the points to the appropriate full advance mark(s) on the rotor ... get it dead on using a meter or continuity checker to verify opening point. Take the rotor back off and remove key. Place rotor at the point of optimum pulse and secure it moderately hard, for testing spark. The key is not needed to make this a secure joint.
Optimum pulse we would expect to be at the point where the rotor and stator poles have overlapped perfectly, where magnetic interaction is strongest. However, a real magneto as found on tractor and Harley usually has the points open at some point previous to that. The practical reason is, we don't want the spark to be fired as the field strength is instantaneously beginning to decline. We want a robust increase in magnetic field interaction to be going on at the rotor/stator as points open, because that means energy will continue to be fed to the spark and even at increasing rate. In fact, the spark continues over about the same angular distance that one pole initially lags the other. So I advise the optimum point be with about 80% pole engagement and correspondingly more if you run some auto-advance.
Make sure points are clean, as magneto performance depends on passing the heaviest possible current thru them. If points are clean and it's wired right it should make spark while turning it over with a wrench. Some degree of tuning is available by putting rotor in different relative positions on crank. After spark intensity is thus optimized, torque rotor down and carefully transfer the timing from the points opening position(s) back to the rotor for your reference marks for next time you work on iggie.