An Absence of Sparks

nighthog

A bit of a bike hacker
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Hello all, I'm trying to help a friend whose bike won't run. Well, it DID, but now it don't.

Bike is an '82 (8/82 on the VIN sticker) that the PO has amended to get rid of the battery box. He welded a tray for the electrics into the frame, so not rubber mounted. The sidestand and headlight relays are gone as is (I think) the clutch relay though the cable from the switch at the lever disappears into the headlight shell - whether it's attached to anything downstream I couldn't say at the moment.
Symptoms are that the motor ran quite happily and then stopped, and now won't run. There are no sparks.
So far, plugs have been replaced, the trigger coils tested (well within range), the coil swapped with mine and so far to no avail. Motor is well earthed/grounded. Kill switch is OK and fuses are sound. Curiously, when keying off there is a spark.
I'm suspicious that the rigidly-mounted TCI unit has given up from vibration, so there's no signal to the coil. I'm not aware of any simple way to test the unit and I've about run out of other ideas. Can anyone offer some thoughts? Have I missed something?

Thanks -
Cliff

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I'll have to ask him - he lives 15 miles or so away from me. The headlight comes on at key on, but I don't think either of us checked horn and indicators.
Agree that the spark at key off is interesting - that's part of what makes me suspicious of the TCI unit.
 
XS motors with non stock TCI ignition systems do spark sometimes if the key is switched on and off. Probe and GN250 do this.
Is the trigger circuit continuous from the pick up to the TCI. TCI magnet still in situ?
 
Is the trigger circuit continuous from the pick up to the TCI. TCI magnet still in situ?
Good point, haven't checked the magnet. I just tested the resistance of the pickup coils at the connector to the TCI and that looked fine; time to whip the LH cover off next time I visit him.
Small matter of my stepson's wedding getting in the way of that though .... I'll be a bit occupied at home until after the weekend!
 
Make sure the sidestand relay AND switch have been removed. That relay acts upon the TCI unit, shorting it out and killing the spark when activated. No need for any jumper wires, you simply unplug and remove both parts.
 
How about the battery .. that can give starting problems if weak.
 
I can confirm that both the sidestand relay and switch have been removed, all other electrics are working fine, and the AGM battery is in good condition.
I'll look at the trigger magnet next week but in the meantime my friend has sourced a TCI unit on Fleabay. At least that's dead easy to swap over now it's not bolted to the bottom of the battery box!
 
I'll have to ask him - he lives 15 miles or so away from me. The headlight comes on at key on, but I don't think either of us checked horn and indicators.
Agree that the spark at key off is interesting - that's part of what makes me suspicious of the TCI unit.
That's normal, to see a spark when the power is shut off.
 
If you are getting a spark when you switch off the key, that means that the tci is energizing the coil and as you switch off the key, the power to the coil collapses, thus a spark. I think the tci should de-energize the coil in the stopped condition, not energize it. It sounds like the tci has issues, but it could also be wiring to the coil. Make sure nothing is shorted. Too bad you are not closer. I could put the tci on the test bench and confirm it.
 
Just had an update from my friend - he's fitted his replacement TCI from Fleabay and the bike now runs. Hooray!! So it WAS the TCI unit after all .... and this time he's rubber-mounted the unit so hopefully there will be no repeat of this saga.

Many thanks to all of you for your contributions - I really appreciate it. And so does my mate :)
 
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