by Richard Axford

For those of a non-technical bent (that’s not a criminal offence, by the way) I have tried to describe the operation of the circuit and ways to diagnose problems correctly. The diagram shows only the important relevant parts of the circuit for a GT750 P5, but I believe the same principles apply to the GTR and GT550. For technical types, the circuit diagram at least might be a help.

First of all, stop looking for a kickstart; there isn’t one (how much beer did you have last night anyway!)
Seriously, I assume that everyone would check that the bike is in neutral, the ignition switch is ON, that the neutral (green) warning lamp is lit and that the RUN/START switch on the right handle bar is in the centre RUN position. If the green lamp won’t light, check the battery voltage. Flat batteries are the most common reason for call-outs to recovery services. The Yuasa batteries should not be below 12 Volts. Still no lamp?.. check that the 30 Amp fuse and the 10 A fuse under the panel are both OK, i.e. not blown open-circuit.

Assuming the above bits are OK, now to the complicated bit...................(please refer to the diagram, which shows wire colours for the GT750).

Basic Operation

Firstly, to make the Starter Motor turn, current must flow from the Battery +ve terminal, through the Ignition and Run switches, the Starter button (when you push it), then through the Starter Control Relay winding to earth (0 V). When this Relay contacts close, it allows current to flow through the Starter Motor Solenoid winding, which closes the heavy contacts and so permits the very high current to flow direct from the battery via heavy cables through the Starter Motor to Earth. Meanwhile, the Ignitor circuit (which initiates the spark at the plugs) also needs to be connected to Earth, via one of the three Diodes. Simple so far? In cars it often is.

You remember I said “........then through the Starter Control Relay winding to Earth (0 V).” ? Well, that’s where I skipped over the trickier bit!!

Circuit Cut-out Operation

There are three switches which combine to allow (or not) the flow of current from that first solenoid winding, or the Ignitor, to Earth, and two of these are probably the most common cause of apparent failure of the Starter Motor. These switches are: the Side-stand switch; the Clutch Lockout switch; the Neutral switch (in the gearbox).

1) Neutral switch.

Mounted in the gearcasing, these very rarely fail; if the Green lamp is lit with Ignition ON and gear in neutral and goes off when the gear lever is moved , the switch is making connection OK.

2) Clutch Lockout switch.

Mounted in the left handle bar lever housing, operated directly by the lever action. If kept clean, these also rarely fail electrically. When the lever is pulled in, the Ignitor and Starter Control Relay winding are both connected directly to Earth, so allowing the Starter to work. If it doesn’t turn, it means the Clutch Switch is not connecting the Y/Gn wire to the Bk/Y Earth wire.

If pulling the clutch lever in makes no difference, the Switch assembly can be withdrawn fairly easily from the lever housing for checking, then if necessary carefully prised open and the contacts cleaned or repaired. A small quantity of Vaseline on the contacts will help future operation. This will save buying a new Switch.

My own clutch switch failed mechanically when the little plastic plunger which pushes on the clutch lever broke off, presumably due to fatigue. I repaired it by using a short length of 12 BA brass screw as a stud, glued into a thread I tapped into each of the two pieces of the plunger. This is now stronger than the original. By the way, I think it is good practice to pull the clutch lever in whenever I start the engine, particularly from cold; it reduces the load on the starter and gives the battery an easier life.

3) Side-stand switch.

It’s this one that usually gives most problems. This switch should make (i.e. CLOSE) when the side-stand is UP; as a safety feature the switch is OPEN when the stand is DOWN. Assuming you have started the engine with the clutch lever IN and side-stand DOWN, when you let the clutch lever OUT this switch is the ONLY route to Earth for the Ignitor circuit, so NO SPARK and the engine promptly stops, which stops you driving off with the stand down. This is very laudable in a perfect world.

Unfortunately, this switch is also positioned low on the bike, in fact in just the right place to get kicked, hit by stones, sprayed with water, grit and all sorts of crap!! This clever bit of design means that the switch contacts can get dirty or corroded, or the plunger broken off, with the effect that when the side-stand is UP, the switch contacts ARE APPARENTLY STILL OPEN instead of closed. Result, the bike runs with the clutch pulled in and a gear engaged (i.e. not neutral), but it stops as soon as you try to pull away!

This is the one that most people get frustrated with, and they have been known to just chop the wires at the switch and join them together. PLEASE don’t be persuaded that this is the only answer, it isn’t. To prevent the need for this, keep the switch body clean and exercise the plunger several times by hand. Once again the switch can be opened and the contacts cleaned. In situ the switch can be sprayed with Electrolube or a similar contact lubricant should do the job. The plunger can be repaired mechanically as described before.