GPZ 900R Ignition system

The GPZ 900R Ignition system

The Ignition circuit on the 900R is fairly straightforward, complexity not being an issue. The difficulty with this circuit lies in it's integration with the starter circuit - many possible earth paths and power supplies are common to both circuits; therefore we must use caution when trying to identify the cause of any given problem. Hopefully the following text will not only explain how the ignition circuit functions, but how the starter and the ignition circuits are linked.

As previously discussed in the article on the starter circuit, Kawasaki have a "safety first" philosophy on the 900R - starting the machine in gear was recognised as a real hazard and so was riding off with the sidestand down!

To prevent the machine being started in gear, Kawasaki designed the starter circuit in a manner, which disabled the start system, if several mechanical conditions were not met. Similarly, the ignition circuit was designed to facilitate disabling the ignition should the rider attempt to pull away with the side stand in the down position.


As we can see from the diagram, power is supplied to the ignitor unit from the battery when the ignition is turned on. In order for the IC Ignitor to function, it must have an earth from either the Neutral Switch, the Starter lockout switch (clutch lever position) or the Sidestand switch.

With the Sidestand down, and no other earth is available to the Ignitor unit, power is supplied to the warning light on the instrument console. If the Sidestand is up, the warning light is extinguished and an earth is provided to the Ignitor unit.

The Purpose of the Ignitor Unit. (CDI unit)

The four main functions of this unit are;

1. The provision or cessation of ignition dependent upon the status of various switches and earth paths on the machine.
2. To receive engine speed and timing signals from the pick up coils.
3. To advance or retard ignition timing according to engine speed.
4. To compute and schedule an accurate timing signal to the ignition coils.

Although these units are usually reliable, they have been known to croak now and then. Having said that, it is often the case to some degree that a problem thought to be originating from the ignitor is, in fact, merely an unreliable signal going into the unit - remember the old saying "garbage in, garbage out" - the Ignitor unit is a computer and will act as such, so care must be taken when troubleshooting.

The benefits of the IC Ignitor system are many fold, the unit is light, small, and like the coils, there are no moving parts - thus reliability is virtually assured .

At Diagram 2, is a much schematic drawing of the ignition system showing relays inside the Ignitor unit. I must stress that this is drawn for clarity and understanding only - the actual unit is solid state with no moving parts whatsoever.
The reason for depicting the internals of the unit in this manner, is to clearly provide an understanding of the various inputs and outputs common to this unit, and how they interact together.


How does it work?

Let us now describe the sequence of events that occurs within the unit, using diagram 2 as our reference.

When the ignition is set to on, power is supplied to the ignition coils and the IC Ignitor unit.

The starter button is depressed and if an earth is available from the neutral switch, or the starter lockout switch, then, and only then will the starter circuit relay energise. This in turn allows the starter solenoid to energise, and we then have battery power to the starter motor and engine rotation begins.

This is a where the starter system hands over to the ignition system, because it is with engine rotation that the CDI unit starts to fuction.

Whilst the crankshaft is turning, a magnet on the end of the crank (termed the "rotor") passes two pick-up coils, 180 degrees apart. A small amount of current is induced into these coils as the magnet passes, and this momentarily energises “relay” A or B.

“Relay” C is energised when an earth is available from the neutral switch, the starter lockout switch or the sidestand switch. With this relay closed, the momentary closure of relay A or B will result in an earth being available to the ignition coils and current flow is established through the coils, resulting in a high voltage delivery to the spark plugs.

Ignition circuit -v- starter circuit

The Sidestand switch has no role to play in the Starter circuit whatsover. It’s primary function is to provide an earth to the IC Igniter unit whilst the motor cycle is in gear, and being ridden. This is the only earth that the Igniter unit can utilise whilst the machine is in gear. Without it, the igniter unit cannot function.

Thus, if you're riding along and the engine suddenly dies, suspect this sidestand switch as the culprit. If the engine starts but will not pull away, this is almost definitely the culprit. As an emergency repair, you can join the Brown/Red wire to the Black/Yellow wire at the side stand switch connection. I carry a scotchlok connector in case I need to do this at the roadside.

Subsequent to any troubleshooting you may carry out to determine the cause of a problem, try a variety of functional checks that may help isolate the components in that circuit as being serviceable or defective. Both of these circuits not only share the same 30 Amp fuse, but the majority of the earths too. It is finding the components that function correctly that narrows the field in where the defect lies.

The IC Ignitor unit itself can be checked with a decent multimeter, full instructions on this check can be found in the Kawasaki manual, although this should be low priority on your checklist - as I stated earlier, these units rarely fail.

Always start troubleshooting with an open mind and be realistic; look at components or wiring that is susceptible to weather, vibration or wear. A moving part is much more likely to fail than its stationary counterpart - such as a relay to an SCR (Thyristor) or a switched earth to a fixed earth. Use logic and refer to the old saying, If stuck call Craig !

Summary - The birth of a spark.

Switch the ignition on and the set the engine kill to run. If this is not switched to RUN, current is not supplied to the Igniter (CDI) unit, or the starter circuit, and the starter will not turn.

Current is now supplied to the Igniter (CDI) unit, and seeks an earth via either:-

A: neutral switch. (Must be in neutral (Green indicator light))

B:- starter lock-out switch (Clutch lever must be in, indicating that although the machine is in gear, the rider has control of it)

The starter circuit relay is energised, which then, and only then, allows the starter solenoid to operate, and supply power directly from the battery to the starter motor.

It is with engine rotation that the IC igniter (CDI) unit starts to do it's stuff.

As the engine rotates, and the magnetic rotor mounted on the end of the crankshaft passes each pulser coil. It induces a small current in each of these pulser coils. This current heads towards the ignition coils via the CDI unit which uses the current to provide a "momentary" earth for each of the ignition coils.

As this current flows through the ignition coil, a magnetic field is induced within the coil' for the period that the crankshaft mounted rotor is passing the pulser coil (pickup triggers). Once the rotor has passed the pulser coil, the "momentary" earth that it has been providing for the ignition coil is removed.

When this momentary earth is removed, the magnetic field that has built up in the coil collapses. As it collapses, it induces a high voltage which is delivered to the spark plug via the HT leads, it jumps the electrode gap of the spark plug in search of an earth which it finds via the engine block.

We have igniton ! Now get out there and enjoy it !