No spark 1990 3TB

[Hatrack]

Thanks Scottieh.
You have reminded me that I have bypassed the clutch switch and the side stand switch. In both cases joing the 2 leads together.
Dreadful thought ! Can this be the source of all my problems ?

[Hatrack]

Unfortunately I binned the cheap Chinese coil. Since it measured up far worse than the original coil. I gave up keeping boxes of unusable parts years ago.
However I did remember that somewhere I had a Dyna coil. I couldn't remember if it was twin or single out put, so I had a dig around and found it.
Twin output, rated at 3 ohms.
Not knowing whether trying it with only one HT lead woud work or not, I hitched it up with a lead, mounted it to the frame and made connections and tried it. Still no spark. Bum.
Not conclusive I realise but it sort of suggests the problem is elsewhere.
I'd be glad if anybody can confirm that my removing clutch switch and side stand switch has not caused the lack of spark.
Its a couple of months ago but I think I dissconnected them after the spark vanished. But there is the possibility that the new TCI has solved the problem but removal of those switches and at each one, joing the wires together, may be still preventing a spark.
I really want to eliminate that possibility.

[dzl]

As long as the neutral switch is lit on the dash the side stand/ clutch switch status is irrelevant. I think you checked the black/ white wire at the TCI plug previously? That wire should be grounded to the chassis when the neutral switch is closed, which it is when in neutral. Also check again the black only wire at the TCI plug, this should also be grounded permanently...so both wires should be 0 ohms at the TCI plugs to the frame.

If you are going to take out the side stand/ clutch switches then you need to short the 2 wires together.

You said you when you put your meter leads on the ignition coil terminals that you had a pulsing voltage of around 6V turning on and off as engine cranked? If this is the case then everything is ok and you should have spark.

[Hatrack]

Thanks.
The neutral is new having just replaced it as the suspected source of an oil leak, but I will check its lighting up the green light.
Yes, I shorted together the wires to those switches, so I'm glad to get 5that possiblity out of the way.
I'll check those readings again.
With the readings from the coil, I would describe them as flickering, rather than pulsing, but holding the 2 probes in place and pressing the start button with only 2 hands its a bit tricky to tell whether the flickerings coincide with the revs.

[Hatrack]

Well yesterday I thought I had cracked it.
I had another go, checking all the earthing and all the live supply and continuity checks, and the multimeter tests as well. Nothing showed any different from the previous tests.
For the past couple of weeks, encouraged by the assurances that "with those readings, there should be a spark" I have been looking for the simple, obvious, damn right stupid oversight cause of the problem. Such as a wire disconected etc. So I checked everything.
And then I saw it !
I had forgotten the most obvious check for an absent spark at the plug that we would always have used before multimeters were dreamed of:
Remove the plug cap from the HT lead and see if there is a spark from lead to earth, AND THERE IT WAS !
So I then weighed up the possible reason. Dud plug cap or dud plug.
I have the original plug cap (with no sign of damage) and a shiny new NGK cap. But as both of these failed to produce a spark at the plug, it must be the plug at fault. But it was a new plug and the bike had been running on it.
Having no spare plug to hand, 15 miles to the nearest bike shop and lean on the counter in time honoured manner, with 2 plug cap and one slightly used plug and the what d'you think ? enquirires. "Its the plug, got to be" says the nice man and sells me a nice new plug.
So I ride home, very happy, and try the plug. Only a tiny, tiny spark visible. Still, it was better than nothing, but not good enough. Fresh fuel, choke on, still won't go !
So it seems to prove that all the multimeter readings were pointing the right way. The major components are producing a spark, of sorts. But why so feeble? Could it be the coil after all ?
Meantime, I've realised, I haven't tried the new NGK plug cap, so there is just one more thing I can try.

[Hatrack]

Checked the new plug cap but the spark behaves just the same.
The spark does not jump from the central electrode to the earthing prong (the bit you would bend to adjust the points gap)
There is only a visible spark from the central electrode direct to the bolt head acting as earth, if it is held very close.
This is something I have never seen before.
Perhaps closing up the plug gap much narrower than standard spec will make the spark behave, but there must be something else causing this, elsewhere in the system.

[Hatrack]

Following the indication that the spark is failing to jump the specified 0.8mm-0.9mm gap that the spark plug is set at, I experimented, closing the plug gap up in 0.1mm steps until the spark jumped its gap.
Finaly, at a gap of only 0.2mm the spark was just visible jumping this way undersize gap.
Optomistically I thought its worth a try, and fitted and connected it but its still a non runner.
My hunch is that the coil is at fault.

[scottieh]

This is great news! At least it's better than before! Following along from the States. Good luck!

[Hatrack]

Well good news at that moment yes.
But the new coil arrived today. Genuine Yamaha item from Fowlers in Bristol. But just the same result.
A feeble, but hopeful looking spark at the HT lead end, but with new or old plug caps fitted and a shiney new plug, it will not jump the plug gap !
So HELP ! Please !

[dzl]

very frustrating! you likely have some sort of resistance in the primary coil circuit causing poor spark performance. Could be a lot of possible issues but firstly I would run a temporary wire directly from 12V + on battery direct to the coil replacing the red/ white wire that normally supplies the 12v feed. This will bypass any possible faulty switch gear that is meant to supply the coil with a positive feed. Do this first and let us know if this improves spark. You didnt say if you checked the resistance of the black wire at the TCI plug to the frame? Should be zero ohms. Is your green neutral light lit when cranking?

If you pay for my flight from oz to pomland I will come and get it sorted for you! Might save you some money!!