No ignition, what have I missed?

[Stevex]

Le Mans 2.
Doubtful it's related but a couple of days ago the fully charged battery could hardly turn over the motor, I put a voltmeter over the battery terminals and the voltage dived to 7v when I pressed the starter, the motor barely turned.
On replacing the battery, I've now found I've got no ignition. No spark at either plug.
I disconnected the molex for the kill switch and con checked it, working normally.
With ignition on I'm getting battery voltage to both coils, which proves the ignition switch and kill switch are ok (doesn't it?).
I have Gammatronix ignition amps fitted, so I disabled them, refitted the condensers and reverted back to normal points ignition, still no sparks.
The only thing different to normal I've noticed this weekend has been on a couple of occasions when the ignition switch has been on and neutral, oil and charging lights have been on, with a very slight rotational pressure on the ignition key, occasionally these 3 lights go out.
However on most occasions it's ok and with battery voltage at the coils, surely this proves the ignition switch and kill switch are working normally.
The ignition system seems to be a very simple system, what have I overlooked?

[fotoguzzi]

I would be digging into and cleaning that ignition switch. It’s pretty old right?

[Stevex]

Possibly the original switch.
I last had it apart about 8 years ago, so I guess it would be a good idea to look at it but if it were faulty I would not expect to see battery voltage at the coils. Is it possible its producing this fault while still providing the correct voltage?
Sometimes I wish I was an electrician.

[nc43bsa]

With a bad connection, you can have good voltage with no load and low voltage with high load.

I think digging into the switch is your next step.

[Stevex]

Just checked the points and with them open I was getting 12+v at each one, so I rotated the engine so each set of points was closed and opened them manually and was getting a weak spark at each set. Checked the spark plugs and now they're sparking!
Bike starts straight away!
Disconnected the condensers, reconnected the amps and their LEDs are indicating...so, I have no idea what's going on.
All I did this morning was remove the tank, points cover and alternator cover, didn't disturb anything and now the bike is behaving normally.

[fotoguzzi]

Um, you also turned the ignition switch on and off? I’d still have a look at that.

[Zenermaniac]

With a bad connection, you can have good voltage with no load and low voltage with high load.

So true.
Decades ago when I was early in my career as a young electronics engineer I had a screwy electrical problem with my car. Spent hours with a VTVM and oscilloscope trying to narrow down the problem to no avail. I described my problem to a coworker who was more of an old school mechanic type and he chuckled and told me to put my fancy gear away and make a test lamp with a tail light bulb. I did and found the problem in 5 minutes. It was a ground connection that looked good with a meter but wouldn’t conduct the needed current. Lesson learned and 48 years later I still carry that test lamp with my tools.
In fact, just recently we had a similar problem with the lights and siren on my son’s vehicle. The test lamp won again.

[Stevex]

Um, you also turned the ignition switch on and off? I’d still have a look at that.

Thats next on the list, there really isnt anything else to check. Just back from a local ride, all good.
I see the bullet connector ignition switches are no longer available.

[John A]

You may be able to get the contact plate for the switch instead of an ignition switch. It is part of the wiring harness and consists of the plate with contacts and a lead with a connector. It is hard to spot in the parts book.

[pressureangle]

Two Septembers ago at the South'n Spine Raid, I had the same symptoms. Long story short, it was the starter. The bearings were seizing, and had been for some time- when I installed the new starter it jumped to life as it never had before. If you have a DC amprobe, check the cranking draw on the starter motor.

https://www.v11lemans.com/forums/topic/23219-starters-batteries/

[80CX100]

I would be digging into and cleaning that ignition switch. It’s pretty old right?

My CX100 is the same age & switch as the OP's bike,from my experience I agree with foto.

When I first got my CX,I changed everything electrical on it and due to a lack of knowledge, got in way over my head.

KiwiRoy kindly took me by the hand and got me and the bike back on track, the very first question he asked me, was had I changed the ignition switch;he recommended it be done as it was almost 40 yrs old.

Sure enough after solving all the electrical gremlins,no joy. Tried cleaning the ignition switch,still funky,

Finally got a replacement ignition switch from MGCycle,the bike's been rock solid ever since.

I'm not saying it's the ignition switch causing your problem,but I'd be inclined to change it and eliminate that as a possibility.

fwiw ymmv 

[Stevex]

Yes I'll be looking into the switch.
If I could get a bullet connected replacement I'd replace it in a heart beat but the only ones I can find are the Zadi ones with spade connectors, unless anyone here knows differently.

[BMCMOTO]

If you are worried about originality or returning to that. You can make a very short adapter by crimping male bullet connectors into open barrel female spade connectors in the wire location, I would also solder them to be sure. You could then use a Zadi switch until you found a suitable early bullet type switch. You could probably have a local locksmith key the Zadi switch the same as your current switch as well.

Brian

[Muzz]

Years ago I did a diagnostic on a Honda CB125 which would keep missing. Went through all the circuits with the multimeter, all good. Got to the ignition switch, isolated it, turned on, all good, turned off then on again, 19ohms. Took it out of the system and the guy went faster in 3rd than he had ever been in top.

Check the ignition switch.