A cough, a backfire, 2000rpm max, now dead

[ianralph]

After a ride to my favourite cafe this morning on my '79 GS1000S I was heading home. Entering the free-way I accelerated to match the speed of the traffic. The bike gave a cough, backfired and lost all power.

I pulled over to the breakdown lane, where I found that I could limp along if I kept the engine below 2000rpm. The bike would idle smoothly, but missed badly and backfired if I try to ride at speeds much faster than 20kmph.

While limping to the nearest service station I found that if I turned the headlight off the engine stopped but would fire again if I turned the lights on. It ran worse if the indicator was on too.

It's now at home - thanks to my long suffering wife and my neighbour who was sleeping off a hangover when my wife woke him up to ask him to help her hitch the trailer.

Interestingly the clock stopped at the time I turned the ignition off and now I see no lights(oil pressue, neutral, charge) nor will the bike turn over when I turn the ignition on.

Any clues about where to start looking for the source of the problem would be appreciated?

BTW the battery is about 1 year old in good condition and was fully charged, bike has standard coils and dynatech electronic ignition.

Thanks
Ian

 

[Ranger]

Have you checked any currents with a multimeter to see if there is any electricity flowing at all, regardless if its enough to power the components?

 

[bobthebiker88]

this sounds a lot like a bad charging system.

 

[ianralph]

Thanks Bob and Ranger - I've put it back in the garage for the moment while I think about it. I'll drag it out again tomorrow and start going over the charging system with a multimeter. I'll let you know how I go.

 

[tom203]

this sounds a lot like a bad charging system.

Yeah, might be one of those cases where Charging voltage is too high. Does it have seperate rectifier and regulator still?

 

[Mith]

Makes me think that the charging circuits wiring was still in it's original configuration where the 3rd wire from the stator routes through the headlight switch. If stator coils 1 and 2 failed then all that was left was 3. When the headlight was turned off it didn't have any current being generated.

Just a theory....

 

[Matchless]

Just a tip, if you have any electrical problems, always disconnect your battery when you get home until you get time to look at the problem. It may save your battery's life if there is a short somewhere which may be discharging it and you only get around to it a month later!

 

[SqDancerLynn1]

I would start by checking the battery, then the charging system

 

[ianralph]

Thanks everyone for the very practical suggestions.

My wife has had me working in the garden today (got to stay in the good books as I've had a few weekends away on the bike lately) so I haven't had a chance to start looking at the alternatives - but I will go now and disconnect the battery.

Ian

 

[Graham]

I'd say a short or open on a rectifier diode or stator winding.
1st Check rectifier then check stator voltage (16.5volt DC).
2nd Check regulator out put (14volt to 15.5volt DC @5000 RPM)

 

[ianralph]

Just to finish this thread. The problem was simple - the main 15A fuse (the top one in the fuse block) had broken. It had not blown: the connection between the fusable link and the end cap had literally broken.

So the part of the charging system that is switched on when the head light is turned on is capable of providing electrical energy to other parts of the wiring. This was enough to keep the ignition working at idle but not above 2000 rpm or under load.

I wonder if this would have been the case with conventional points ignition? (I have a Dynatech ignition)

You learn something new everyday!

Thanks to everyone for posting suggestions.

 

[7981GS]

Thanks for posting the solution.
It may very well save others from some head scratching in the future.

Daniel

 

[DanTheMan]

Hey Ian, I just saw this thread. I had the same problems with the old fuse blocks (yeah, I went through two of them). I replaced the glass fuses with a blade type fuse block, which I'll probably replace again with a better one next year. The one I bought is an expensive cheaply made piece of junk. We've got snow everywhere now, enjoy your summer weather, my wife says we need to get out of this stuff sometime, go where it's warm when it's cold here.