40 Electronic ignition
Only those dedicated to originality can ignore the benefits of electronic ignition systems for classics. Fiddle with points? We (Rick excepted) would rather not. Plus, modern fuels make electronic ignition even more useful.
To understand its benefits, a reminder of the workings of basic points ignition is useful. With the points closed, current flows through the primary winding of an ignition coil, inducing an electro-mechanical field around it. When the points are mechanically opened, this electro-mechanical field collapses and induces a high-tension pulse in the ignition coil’s secondary winding which provides a high-voltage, low-current spark across the plug gap. A condenser (capacitor) at the points prevents arcing across them rather than the plug gap.
For starting, the spark has to happen later in the combustion cycle (retarded); then, as engine speed rises, it needs to happen sooner (advanced). The familiar battery and coil systems use an automatic timing unit, which allows the cam that opens the points to rotate, the amount it moves being controlled by bobweights on springs that are flung outwards as engine speed increases. While the physical arrangements of a basic battery/coil system and a magneto differ, the physics and what the contacts do is broadly the same.
There are some major pitfalls – the mechanical nature of the system makes it prone to wear and fall out of adjustment. Eventually condensers fail, too. Plus, even at 20,000 volts in a battery/coil system, fatter sparks are always useful.
Enter electronic ignition. The first capacitor discharge ignition (CDI) systems used a rotating trigger with a magnet(s) passing by fixed pick-up(s) instead of cam-operated points. The pick-ups sent pulses to a CDI box, the capacitor therein discharging through the primary windings of the coil and inducing high voltage in the secondary as before, only now up to twice as much. Advance/retard was first taken care of by secondary pick-ups offset, then later by measuring variances in induction in the pick-ups at different engine speeds. As systems evolved, transistor and then digital technologies were used to control voltages applied to the coil primaries as well as advance/retard curves. Different triggers and pick-up systems emerged to join the magnets and coils.
Boyer Bransden have been into electronic ignition since 1969. Their systems have inspired others and even been adapted into mag replacement units by other firms, while product development has taken advantage of modern tech culminating in the current Micro-Digital and Micro-Power offerings. These, like many modern systems, can operate at sub-par voltages; an advantage not least when cranking an engine over on a current-hungry electric starter. All that tech starts at a reasonable £140 or so. Pazon point
