Engine cut, '82 R100RS

[John Roberts]

On my way home this evening the engine stopped while waiting at traffic lights. It eventually started before the lights turned green, but stopped again after another quarter of a mile. It was running just fine up until then.

I took a plug out and had a look at the spark, it was weak, whitish, not blue, and intermittent. The funny thing was, however, that there was always a spark when I switched the ignition off or on.

All this was at the side of the road, I only had the original tools in the wallet.

I called a mate and left the bike at his place, the wiring diagram is still with the bike, so I'm scratching my head, but I'm wondering if it could be anything to do with the Hall effect trigger: ign on/off = spark always, spinning the engine on the starter = occasional spark.

Any suggestions?

 

[Beemerboff]

Don't rule out the ignition switch - I had similar symptoms which were down to poor contacts in the switch.

In my case the problem was visible once I had the switch off - the black plastic block which is crimped into the back of the switch was loose.

 

[John Roberts]

Does anybody think I could be right about the Hall effect/contact breaker thingy? The reason I'm suspecting that is because when I switch the ignition on and off there is a spark (as is normal) but the fact that there isn't a spark when the Hall effect thingy is doing the same thing, i.e. making and breaking the circuit, it fails to produce a spark. If the fault is indeed with the ignition there are some expensive bits involved and I don't have any spares to substitute so any informed guidance would be appreciated- f'rinstance if I'm talking bollox then I'd like to be told. Please?

I haven't been back to the bike since it broke down, but what I did find at the time was that the fuel was coming through OK to the carbs, there was no water in the float bowls, and while trying to restart there was a backfire, so I'm thinking that fuel was getting to the cylinders and being ignited by the intermittent spark. I also took the tank off to look for any tracking at the coils while spinning it over but saw nothing.

Anything else I should look for when I get back to the bike?

 

[casper]

Had similar symptoms with my 82 RT except I had no spark at all when spinning over and nice fat spark when turning ignition on and off. I was lucky as I had a spare "bean can " which sorted it out.Try this link for more info on rebuilding yours. Also carefully check all related wiring first. http://www.deathstar.org/~flash/ig_trig.html
It was the only time mine broke down in over 100,000m of ownership.

 

[John Roberts]

Had similar symptoms with my 82 RT except I had no spark at all when spinning over and nice fat spark when turning ignition on and off. I was lucky as I had a spare "bean can " which sorted it out.Try this link for more info on rebuilding yours. Also carefully check all related wiring first. http://www.deathstar.org/~flash/ig_trig.html

Thanks for that, encouraging. Good point about checking the wiring first.

... It was the only time mine broke down in over 100,000m of ownership.

I was talking to somebody about the bike yesterday lunchtime, he was asking how it was going, as one does. I said it had never let me down in 76,000mls apart from one of the little springs on the selectors breaking twenty nine years ago, and said that there was nothing much to go wrong on airheads anyway, they just go on forever ...

 

[John Roberts]

Update

Some feedback for future reference: It was the "Bean can"/ Hall effect trigger unit.

Thank you both.