Motom Ignition: From the Motomic Magnet to the External Coil on Sport Models

The evolution of Motom’s ignition system is one of the most underappreciated technical aspects in Motom’s history. From the small magnet used on the first Motomic in 1947 to the adoption of the external coil on Sport models and agricultural applications, the Milan-based manufacturer developed various solutions over the years, all characterized by simplicity, reliability, and ease of maintenance.

The 1947 Motomic and the small magnet in the crankcase

With the first Motomic, introduced in 1947, Motom adopted a solution that was already widespread in the motorcycle world at the time: magneto ignition.

Unlike the systems that would be introduced in subsequent years, the magnet was a self-contained unit capable of directly generating the energy needed to ignite the spark plug. For lighting, however, a separate dynamo system was used, conceptually similar to that found on bicycles of the time.

A little-known fact is that the Motomic’s magneto was extremely compact—probably one of the smallest ever used on a production motorcycle. Even more curious was its location: the unit was completely enclosed within the engine casing.

Even today, when looking at the casings of later Motom 12A models, it is still possible to identify the location originally intended for this component.

The switch to the magnet flywheel, the new Motom ignition system

With the 12A model, Motom abandoned the separate magnet and adopted the magnet-flywheel system that would come to characterize all subsequent production.

The cast housing initially retained the shape of the old magnet housing, but it was no longer machined. The generation of electricity was handled directly by the permanent magnets embedded in the flywheel.

As it rotates, the magnets generate a varying magnetic field that induces a current in the coils attached to the stator plate. In addition, the flywheel itself generated power for the lighting system via a dedicated coil.

There were numerous advantages:

lower production costs;
fewer components;
greater compactness;
simplified maintenance;
Simultaneous power supply to the ignition and the lighting system.

How the combined LV/HV coil works

For many years, Motom motorcycles used a combined coil that integrated both the low-voltage (LV) and high-voltage (HV) circuits into a single component.

There were two windings on the same magnetic core.

The primary winding, consisting of just a few turns of wire, generated the low-voltage current. When the pins break the circuit, the magnetic field collapses rapidly.

This phenomenon induces a very high voltage in the second coil, known as the secondary coil, which consists of hundreds of turns of very fine wire. The high-voltage current then reaches the spark plug, producing the spark needed to ignite the fuel-air mixture.

The capacitor connected to the electrodes limits the electric arc and causes the magnetic field to collapse more quickly, thereby improving the efficiency of the entire system.

This simple and economical solution remained the standard for most European mopeds until electronic ignition systems became widespread in the 1970s and 1980s.

The ignition system that was fitted to nearly the entire Motom lineup

For many years, all street motorcycles used this system.

The coil, pins, and capacitor were mounted on the plate behind the flywheel, forming a compact, self-contained unit.

The benefits were clear:

very simple electrical system;
few external links;
low costs;
ease of assembly;
good protection of the components.

For this reason, the solution continued to be used on the GG and C models as well, even though the lineup already included sportier models equipped with a different ignition system.

The Introduction of the External Coil on Motom Sport Motorcycles

The evolution came with the sportier models, such as the SS and Junior.

In these versions, the high-voltage conversion no longer took place inside the coil mounted on the flywheel. The high-voltage coil was moved to the outside of the engine, usually beneath the fuel tank, while only the primary coil remained beneath the flywheel.

The operating principle remained the same, but separating the components offered several advantages:

improved accessibility;
faster reel replacement;
less exposure to heat;
easier maintenance.

Why was the external coil also used on Motom tillers?

The external design of the Motom ignition system was also featured from the outset on engines intended for tillers and agricultural applications.

In this case, the reason was mainly practical. The presence of air ducts and cooling fairings made it difficult to route the high-voltage cable coming from inside the flywheel.

The use of an external coil allowed for simpler wiring, greater accessibility, and faster maintenance directly in the field.

Low-voltage coil (top) mounted on a base plate

A technical advancement focused on simplicity

For several years, Motom continued to offer both configurations: on the one hand, traditional models with a combined low-voltage/high-voltage coil integrated into the flywheel; on the other, sports and agricultural models with an external coil.

Two different solutions, both consistent with Motom’s design philosophy: simple construction, reliability, and ease of maintenance.

The evolution of the ignition system clearly illustrates the technical progress the company has made, from the tiny magnet in the Motomic to the most advanced configurations with external coils.

In the next article, we’ll explore why many enthusiasts who regularly ride their Motom bikes are now choosing to install an external coil and an external capacitor, what benefits this modification offers, and how to do it without irreversibly altering the bike’s original condition.