This will explain the types of ignition system components and their function....


All gasoline engines require an ignition of some sort. In it’s most basic form, an ignition system consists of a set of breaker points, a condenser, a coil, a spark plug, and, a voltage source. Let’s set up a sample single cylinder engine with a breaker point system.

First, we need to understand what the different components do.

The coil consists of a set of primary and secondary windings. The primary windings (12 volt or low voltage) are wound around a core made of thin iron plates or solid iron. The secondary windings (High voltage) are wound are around the primary windings separated by a layer of insulation. The current needed to jump across the spark plug and ignite the mixture is generated here. Basically, voltage is applied to the positive side of the primary windings and grounded through the breaker points on the other side. As long as the points are closed, voltage flows through the windings, a magnetic field is created, saturating the secondary windings. The the primary windings are isolated from the case and only ground at the points. When the breaker points are opened, the magnetic field collapses and current is generated (induced) into the secondary windings. This current travels from the coil to the spark plug and jumps the gap, creating the spark. Once the field is collapsed, The coil must re-saturate in order to create another spark.

This is where the points come in. On one side of the points, there is a terminal where the lead from the coil connects. The other side of the points are grounded. There is a camshaft with a lobe that lifts the points and breaks the connection to ground. The width of this gap and the length of time they stay apart is the point gap and dwell. There is a condenser connected to the points to prevent arcing and increase the life of the contact points. Whenever the points are closed, the circuit through the coil is completed. The magnetic field is created, saturating the coil. Open the points, the field collapses and the spark is created, jumping the spark plug and igniting the mix. The opening of the breaker points is timed so the spark is created just before the piston reaches the top of the compression stroke. There is a mark on the crankshaft (flywheel on Harley Davidson Motorcycles) that tells us when the engine is at Top Dead Center (TDC). TDC is when the piston is a the very top of it’s movement on the compression stroke. Since there are 360 degrees in a circle, we can set the timing at any point and know exactly where it’s set by using a timing light. Usually, the spark needs to occur slightly before TDC to make the most power. We also need to have some sort of method to advance and retard the timing to prevent detonation (pinging). As RPM increases, the amount of advance must be increased. Since the pistons are moving faster, there is less time to burn the mix. So, the spark must be started sooner to make the most power and prevent detonation. In our sample engine, we use a simple weight system that moves the breaker point cam in relation to RPM. The amount of advance graphed against RPM is known as the advance curve.

Note: Detonation occurs when the spark explodes the mixture rather than burning it. This explosion is extremely detrimental to your engines health. It sounds like a "pinging" noise when you accelerate. Detonation will destroy an engine. If you hear it, check for proper timing, too low of an octane rating gas, or air leaks.

A magneto ignition works in much the same way, except there is no need for a battery as current is generated by a permanent magnetic armature rotating past the field windings, creating the spark. Magnetos are self contained and create an extremely powerful spark.

On our sample engine, we have a 12 volt battery which provides power to the positive side of the coil through the ignition switch. On the other terminal of