The Alternator is made up of the stator and the rotor.  The stator is six coil windings connected in series.  Each of the coils has a different number of windings.  The rotor is a six pole magnet that is attached to the engine sprocket.  As the rotor spins, a combination of the different number of coils of the stator produce different levels of voltage, which in turn power different parts of the bike.  The high voltage output, for example, could be used for powering the spark plug while the low voltage output could be used for the brake light.

The points act as a physical switch to regulate the timing of the spark plug.  As the motor spins, the cam (the slightly oval piece in the middle of the picture below) spins with it.  The purpose of the cam is to open the points at the appropriate time.  It does this by pushing the hammer-like piece back each turn.  Adjusting the cam correctly is very important because the points must be precisely timed to spark the spark plug at the proper time and prevent pre-ignition.  At high speeds, small weights on the centrifugal advance mechanism also advance the timing of the points and makes the spark plug fire slightly earlier.  This compensates for the fuel having less time to burn as the engine reaches higher speeds.

The coil consists of two coil windings.  It is a transformer that provides the step-up voltage obtained from the points needed to spark the plug.  When we received the bike, it used a battery ignition coil system.  Because a battery provides DC current, the old coil was a DC coil. Now, our bike uses an energy transfer system, so it uses an AC coil.  The coil operates on the principle of induction which is covered in the Physics Review section.

The spark plug is what ultimately ignites the fuel in the engine.  The spark plug uses the high voltage current that is produced by the coil to spark across the “spark gap.”  It is important that the spark occurs at the right time to maximize efficiency.

We originally did not have a wiring diagram, so we tested each connection manually. After some searching, we found this diagram that tells us what each wire is connected to. On our bike, the horn button serves as the kill switch.  

All of these key components come together in the wiring harness, which is the network of wires that supplies power to each part of the bike. The next page of this website gives descriptions of the wiring harness and its construction.

Here we have a software simulation of the electrical circuit that powers the bike. Many key components such as the alternator, points, coil, and spark plug appear in the circuit. A detailed description of the physics of this circuit appears in the physics/theory page of this website.

There are several parts that are necessary for the electrical system to function.  They are, briefly, the alternator which provides power from the motor, the points that regulate the timing of the spark plugs, the coil to increase the voltage from the alternator to the spark plug, and the wiring harness to distribute the power.

Link to circuit simulation