Intermittent ignition problems

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Rob Frankhamr
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Re: Intermittent ignition problems

Postby Rob Frankhamr » Wed Aug 14, 2019 10:06 am

That's a good reference... but... it doesn't and can't address the fact that this fault is intermittent. You can only effectively troubleshoot an electric problem when the circuit isn't working properly and, in this case, this will almost inevitably be at a time and in a place where formal troubleshooting is at best inconvenient.

For my part, as an initial and to a certain extent pre-emptive measure, I would check every connection in the ignition circuit and make sure they are all tight and clean. I would then work my way through all of the wires pushing, pulling and wiggling them to see if I could replicate the problem. This would need to be done with the engine running so it would be necessary to rig up a 'remote' fuel supply (in the past, I have achieved this by removing the seat and resting the tank on the subframe with extrs fuel hose to the carbs). If that doesn't produce any results, I would always carry a multimeter and/or test light in the hope that, should the problem occur again, I could carry out some diagnostic tests before the problem, whatever it is, goes away again.

FWIW, I had exactly this situation with my old R45. I would be riding along when the engine would cut out then, after a certain amount of time (sometimes even before I'd come to an involuntary halt) it would go back to normal. The only difference I can see with Petes issue is that the bike was completely dead when it cut out... no electrics at all. If I 'solved' it once, I 'solved' it a dozen times, loose battery terminal, dirty igniton switch connectors etc. etc. but, every time, it would come back again.

The 'lightbulb' moment was when, one day, the problem occured yet again and I ground to a halt... then I happened to move the handlebars and everything came on. Turned out that the problem was the main feed wire from the battery to the ignition switch. This had broken in the loom and was making intermittent contact by touch. When movement of the handlebars or vibration made the wire ends lose contact the bike died. another slight movement made the wire ends touch and all was back to normal. The fix was easy enough... just run a parallel battery feed wire but diagnosis was a grade a class 1 PITA.

Not saying this is the problem here (although it might be), just trying to put over the difficulty of diagnosing an intermittent fault and the importance of observing all of the symptoms, (expecially where they affect other circuits).

No, I'm sorry Pete, I don't have a simple answer...

Rob
Robin Frankham
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ptjenkins65
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Re: Intermittent ignition problems

Postby ptjenkins65 » Sat Aug 17, 2019 8:37 am

Thanks Rob, that is a very sensible answer. It’s the occasional nature of the problem that’s is most niggling.
The other problem being that the bike is at our place in Italy and I am back in the UK so I can’t just pop to the shed and have a look. When it was in the UK it was just fine. When I get to it I’m will have a good wiggle of all the cables and junctions to see if I can get it to do it again, if it will start at all.
And the white spark, is that an issue too?
Pete
1998 r850r
1979 r45
1974 r60/6
Still learning

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Rob Frankhamr
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Location: Kinloch Rannoch, Perthshire

Re: Intermittent ignition problems

Postby Rob Frankhamr » Sun Aug 18, 2019 10:41 am

Judging the colour of the spark is at best subjective. I would say that a yellowish spark would be a weak spark, a white spark tending to blue would be moderately strong, certainly strong enough to light the fires in the cylinder. This is born out by what you say in your original post... when the bike stopped there was no spark... as soon as the spark came back, the bike ran. Once started, an engine can run with quite a weak spark so I'm of the opinion that the 'white' spark' you refer to probably isn't a root cause of the problem.

Rob
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