Electrics diagnosis please.

[hzbloke]

1986 R65, 300,000km, all original electrics (afaik) apart from coil which is from something Japanese and was there when I bought the bike 100,000km ago. About 1,000km ago new guides & valves, timing chain and carby kits.

Off on a trip and the bike's running beautifully. At a petrol stop after about 200km everything was beaut - idling well, started at a touch of the button. About 100km further on I'm stopped by a man with a stop sign (turns out to have been a fatal accident up ahead) and the bike cuts out before I come to a stop. It starts OK. I stop at the next town to see if there are any obvious problems. The bike cuts out at low revs and won't start.

Off with the tank and jiggle wires etc. Remove a plug and there is spark but very weak looking. Can't find anything so put it back together. It eventually starts. I decide to press on to my destination.

Running fine but perhaps, and only perhaps, a very slight cough in the exhaust. So faint I can barely hear it. After about 50km it cuts out and doesn't start again. It came home on a trailer.

Any suggestions as to what it may be would be appreciated.

[Kurt in S.A.]

I wouldn't rule out the that the valves have closed up. Difficulty idling is a sympton of tight valves. Easy to check. Then move on to electrics.

Kurt in S.A.

[Deleted User 62]

Did you retorque the heads and adjust the valves after the first warmup, and then again in a few hundred miles? If so, I suspect the coils. When you checked for spark, did you pull the plug and ground it to the engine? Not doing so can do bad things to electonic ignitions.

[SteveD]

Coil came quickly to mind.
Then I wondered about the heat sink on the ICU, the bean can and even the ignition switch playing up.
Do you think it's something that gets better when it cools down?

[hzbloke]

I checked the valves 3 times and did the heads once in the 1000km since they were installed and I have compression so it's probably not them. Also the bike cut out abruptly which I don't think would happen with valves.

The ignition switch was new about 10,000km ago but, of course, that doesn't mean it's OK.

Yes, I did make sure both plugs were earthed. What is actually damaged if they are not?

I did the heat sink paste about a year ago. I also wondered if it was heat related but it's been cooling down for over a week now and still won't start so I'm tempted to rule that out.

I won't have time to get the multimeter out until later in the week so at the moment I have no further info to offer.

Cheers and thanks
Ray

[SteveD]

What does it do when you try to start it now?
With ignition to on, and with the starter button depressed, does the tacho needle move at all?
Any slight movement? If not, I'm thinking bean can.

[Motu]

Not experienced with these BMW things - but very experienced with cars using ''ignition modules'' such as fitted to this bike. This is classic module fail - at low speeds the module starts current control, limiting the amount of current going into the coil, and gets rid of it through heat. The engine stalls at idle, and starts up straight away or after a slight rest, just long enough for the module to cool down. Factors that contribute to module fail are plugs, leads and coil.

[SteveD]

Factors that contribute to module fail are plugs, leads and coil.

I have a spare icu (from Grant when he sold his bike) if you need one quick to test.

[jagarra]

If this bike has a points ignition, I would suspect the condenser. If it has modules associated with the ignition, maybe one of them. I had an intermittant problem on one of my bikes, turned out to be corrosion on a voltage source connection that was feeding the ignition system.

[mattcfish]

Sounds exactly like what happened to me when my alternator rotor failed (opened). A flaw in the BMW design is that, if this happens the red charging light will not light to warn you. You'll just keep riding until the battery is completely drained. You won't notice until you come to a stop or the battery is completely dead. You can go a long way on a battery charge, so if this happens to you, grab any 12v battery you can strap or bungy on and you might make it home (or recharge the one on the bike overnight).
I'm 99% sure this is your problem. Another thing that can happen is that the charge light will burn out. The bike won't charge if it's burned out....really. You can test that by just turning the ignition on without starting. The charge light should light. If your alt rotor is "open" you can test it easily with a multimeter. With the brushes pulled, resistance on a bad rotor between the tow rings will be infinate. On a good one it's 2. something ohms I believe.