Bike won't start but starting system tests ok?

Falco · Traffic Copper Joined: 26 Nov 2015 Karma :

As the weather has turned colder, the bike (CB500S) has been getting funny about starting. Not in the "struggling to start way" but simply doing nothing when I hit the starter, no dip in the headlights, just nothing, only coming to life after the button has been hit several times.

I traced the problem to the starter switch, and a blast of WD40 fixed it enough to keep it running for antother week, but the problem started creeping back in from Wednesday.

It's rather odd, since once started, it will sometimes work on the first press and sometimes not.

Took the tank off and the solenoid checks out as fine (continuity between terminals when 12V is applied to the little connectors -the low voltage side?- and a loud click).
The switch works fine at the switch side of the connector block, the red/yellow wire has continuity from the bike side of that connector all the way to where it plugs into the relay. The red/green connects to a whole load of things on the diagram so I am not sure how I would check that wire.

Oh, and when the starter switch is hit, there is no voltage showing between the -ve battery terminal and the starter relay terminal (though there is continuity).

I'm running out of ideas for what the problem might be? I'm going to test the starter motor, but mostly because I can't think what else to do.

Any ideas gratefully received as I'm pulling my hair out a little at this point.

PS Battery is at 12.7V idle (was at 12.9V before I started trying to crank the bike, trigger the solenoid etc)

EDIT: starter motor fine, bridged the gap with screwdriver, then jump leads and it spins happily. Continuity between solenoid and starter motor.
Now at a total loss, every individual component seems to work, but the system as a whole does not Doh!

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I tell you what, mathematically, I'm having it

Kawasaki Jimbo · World Chat Champion Joined: 09 Oct 2015 Karma :

Falco · Traffic Copper Joined: 26 Nov 2015 Karma :

ZebraDriver · Scooby Slapper Joined: 13 Feb 2011 Karma :

"circuit is showing continuity when pressed". It may be that the button makes continuity when connected to a meter but fails when the load imposed by the starter solenoid is put onto it. Check that 12 volts shows up at the solenoid when the button is pressed.

Falco · Traffic Copper Joined: 26 Nov 2015 Karma :

There is no voltage showing at the solenoid when the button is pressed (between the battery and the solenoid is what I mean). Is there a way to test the switch under load?
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I tell you what, mathematically, I'm having it

bikenut · World Chat Champion Joined: 21 Nov 2011 Karma :

Are the lights misbehaving like the neutral light flashes when the handlebars are turned from lock to lock, any other lights/horn do this at all??

You have a wiring diagram ? post it if so.
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nuts about bikes

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

So the bike turns over when you bridge the solenoid with a screwdriver, but often does nothing at all when you press the starter button.

This means your problem is in one of the following areas:
1. Battery. Always the first port of call, because its easy and this is battery death season. Stick it on a charger, then immediately try to start the bike. Batteries lose capacity as they age. They can still show a good voltage, but are only producing half the current they did when new.
2. Solenoid. Solenoids can suffer from corrosion, making them a bit sticky and difficult. Bridging the terminals bypasses the bit that fails, so it isn't a way of testing the solenoid. A knackered solenoid will generally work better if it has plenty of power being supplied. A pattern replacement is cheap. May even be possible to strip and clean the existing one.
3. Switch. Whilst these can fail, its fairly unlikely, and it looks like you've tested the switch with a multimeter and sprayed in some WD40. Simply operating the switch a few times with some WD40 on it will clean the contacts up a bit.
4. Wiring from switch to solenoid. If there is an internal break in the wire, then it may work when the bars are at one angle (like dead ahead), but not at another angle (like right over to the side) because the internal break is getting pulled apart/pushed together. Can be tested by having a multimeter on the switch looking for continuity as you hold down the switch and move the bars side-to-side.