GPZ 900R Starter Circuit


It is important to understand that the Kawasaki engineers developed the starter circuit with safety being a primary objective. The main philosophy centres around the danger that arises when the starter motor is energised with the bike in gear and the clutch engaged. Because this was a common occurrence on other, earlier motorcycles it was recognised as a real hazard so Kawasaki decided to design a circuit that was foolproof - in other words, the starting of the engine whilst the machine was in gear was simply not possible.

The logic behind this system is very straight forward, - so long as the "drive" is engaged you cannot start the engine.

This essentially means that the engine can be started with the bike in gear, as long as the clutch is disengaged, (lever in) or, the engine can be started with the bike in Neutral, whereby the clutch status is irrelevant. Simple !

Please note that sidestand switch position has No role to play in the starter circuit.

System Description and Operation

The circuit consists of two Relays, the Starter circuit Relay and the Starter Relay. Two Switches are employed, namely the Starter Lockout Switch and the Neutral Switch.

The Starter Circuit relay is Located in the junction box and is the lower of the two circular relays. ( Most of the workshop manuals refer to 3 x relays, however most GPZ 900R's only employ 2.) The Starter Relay is located just forward of the junction box and is the lower of the two rubber sleeved relays. The Starter Lockout Switch lives underneath the Clutch lever assembly, and the Neutral switch sits adjacent to the oil level sight glass.

In order for the Starter Circuit Relay to operate, it relies upon an earth signal being provided by either the Starter Lockout Switch, or the Neutral switch. The starter Lockout switch, is located on the clutch lever assembly, and, when the clutch lever is pulled in, an earth is provided from the main electrical system ground. With the Clutch lever out, the earth is obtained through the Neutral switch (providing of course that the gearbox is in Neutral).
Suffice to say, that if the clutch lever is out, and the bike is in gear, pushing the starter button will have no effect!

What should happen?

With the ignition on, and the Starter button depressed, power is supplied to the Starter Circuit Relay from the battery, and, provided that the Starter Circuit Relay is supplied with an earth signal, it will then provide power to energise the coil in the Starter relay which has a fixed earth. The contacts in the Starter Relay will then close, and Battery power is routed to the starter motor.

Troubleshooting the system

Okay, so the Ignition is on, you've pressed the starter button and nothing happens. Let's do all the basic checks first:

Is the engine kill switch set to run?
Is the Green Neutral light illuminated?
Does the battery have plenty of Volts?

Let's assume that you answer "Yes" to all of the above.

Use the trouble shooting guide below, but bear in mind, that this guide is designed to prove the starter circuit's components, and as with all things electrical, chafed wires, poor earth's and cunning wiggly's may feature in any problem you may experience. Electrical problems are often very difficult to locate and solve.

To Prove the Starter Circuit Relay

This is easy, remove the Main relay, (which is above and to the right of the starter circuit relay) and swap them over. These relays are identical, and can be interchanged. The bike will start and run without the main relay, but you'll have no electrics. ( Nb :- Many of the workshop manuals show 3 x relays, whereas the majority of GPZ 900R's only utilise 2)

To Prove the Starter Relay

Again, relatively simple to prove. Turn the ignition on. Disconnect the small plug on top of the starter relay, and with the starter button pressed, check for a 12V supply between the Red/Yellow wire (+'ve) and the Black/Yellow wire (-'ve). Refit the connector. This is the (switched live) power feed to the starter relay which of course is activated by the start button.

Press the Start Button once again, and this time check for a 12V supply on the "Out." terminal of the relay. Ie, the wire that feeds down to the starter motor, this is on top of the relay, on the left, and has a rubber cap on the terminal.

To Prove the Neutral Switch

Simplest of them all, it does most of it itself! With the machine in Neutral, and the ignition switched on, is the Green Neutral light illuminated on the instrument cluster? If it is, then the Neutral indicator switch is working. If it's not the bike may be in gear, the bulb blown, or the switch faulty. If the Neutral switch appears to be faulty, disconnect the light Green wire from it, connect the wire to an earth, and attempt to start the machine, if it starts, the neutral switch is faulty.

To prove the Starter Lockout Switch

Assuming that the two relays are serviceable, and that the neutral switch is serviceable, turn the ignition on, pull the clutch lever in and press the start button. If the machine fails to start, the starter lockout switch must be considered to be at fault, or another fault exists elsewhere within the circuit.