Description

If motorcycle electrical work sends "shocks" up your spine, fear no more! The Motorcycle Electrical Manual, (3rd. Edition) by Haynes, is here to help. This manual, intended for the do-it-yourself home motorcycle mechanic, covers and explains, in simple terms, all areas of motorcycle electrics, including:

Ignition and combustion
Spark Plugs
Coils
Magnetos
Batteries
CDI (Capacitor Discharge Ignition)
Transistor ignitions
Digital ignitions
Alternators
DC generators and starters
Lights and signal systems
Braking and traction-control systems
and much more!

The manual also includes chapters on electrical troubleshooting as well as testing and required test equipment. In short, a must-have book for technicians and home mechanics who want to tackle motorcycle electrics.
Book Excerpt: Motorcycle Electrical Manual: Ignition, Combustion, Plugs, Lights, etc. | Haynes IGNITION | COIL AND BATTERY

SETTING THE CONTACT BREAKER GAP

Start by removing the spark plug(s) so that the engine may be turned over easily. Note that motorcycles have one, two or three sets of points, but the method of adjustment is the same for each.

To check the gap the engine must be rotated by one of the following means:

Apply hand pressure on the kickstart (where fitted).

Use a spanner on the engine turning hexagon on the end of the crankshaft or alternator rotor.

With the motorcycle on its mail stand, turn the rear wheel by hand with the engine in a high gear.

Turn the engine until the contacts open to the maximum and insert a feeler gauge which corresponds to the recommended gap between them. If no information is available, try a gap of 0.3 ? 0.4 mm (0.012 ? 0.016 in). The feeler gauge should just slide through the gap between the contacts with a slight drag. If too tight or too loose, slacken the baseplate screw so that the fixed contact may be moved to give up the correct gap. This is done with either a flat-bladed screwdriver twist in a slot or by turning an eccentric screw. When the gap is correct tighten the baseplate screw.

If the engine has more than one set of contacts, repeat the process. It is worth rechecking the gaps after the engine has been turned by hand a few times.

Setting the gap by feeler gauge can give satisfactory results if done carefully, but accurate setting is vital, particularly on high performance engines. A better method is to use a dwell meter.
USING A DWELL METER
The real purpose of setting the gap correctly is to ensure that the contacts are closed long enough during an engine cycle for current to build up in the ignition coil primary winding.

With the engine running slowly, a dwell meter connected to the contacts will read the angle of rotation during which the contacts are closed and give the reading in degrees or percentage dwell. The correct figure can be found in the workshop manual. An inexpensive meter is the Gunson Sparktune (see paragraph 4) which will read dwell accurately, check contact resistance and act as a useful voltmeter (see illustration 9.11).