C&T Publications REVOLUTIONS II - April 2015 | Page 58

Ignition Failures and Solutions for Classic Motorcycles
by Paul W Crowe

In the quarter century that I have worked at dealerships and owned classic motorcycles one certain fact has emerged - ignition
systems fail.
The "How and Why" are often a mystery, even to some mechanics. The goal of this article is to educate you about the function of an
ignition, explain the cause of common failures, and review current solutions on the market today.

What parts make up the ignition of a motorcycle?
Three parts: Coil, ignition trigger, and spark plug.
Most motorcycle coils look like a can of soda with spark plug wires sticking out the end. The function is simply to convert your 12
volt battery power to a much higher voltage that can fire your spark plugs.
All ignition systems have a trigger of some kind, either a mechanical "points set" or magnetic sensor to turn the coil on and off at the
correct time.

How does an ignition work?
On older engines the contact points open and close using a spinning lobe mounted to the cam or crankshaft. When the points
CLOSE, power flows through the coil creating and storing high voltage energy.
It takes a certain amount of time (lobe rotation) to charge up the coil. The amount of rotation needed is called Dwell and is critical to
proper coil operation.
Too little time=engine misfire from lack of coil energy
Too much time=excess heat and eventual coil failure
When the contact points open , it shuts the coil off causing the high voltage energy field to collapse, travel down the spark plug wire
and make your plugs SPARK.
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