Misfiring GS Ignition Question

[Deleted User 62]

A friend here on the island had a bit of a problem with his 1990 GS. He was riding along and the bike began misfiring and made a loud "bang". He rode it for a few miles this way back to his house. Upon closer inspection he found a sparkplug wire had loosened from the coil end. I know it was probably the unburned gas in the exhaust that made the banging noises . My question is this, I've heard that running an electronic ignition without the sparkplug connected can damage the electronics. What are the chances he fried something in the bean can? Would damage show up as weak or no spark? Note: he has the dual output coil. Would the fact that the other cylinder was firing mean the spark on the missing cylinder have a place to go? In other words, are the dual output coils lighting both plugs at the same time? Thanks in advance!

[Major Softie]

There are different kinds of electronic ignitions. Some are very susceptible to damage from not having the spark grounded out, some are not. When it can do damage, it is not the coil that gets damaged (at least not in a system that uses a conventional coil like the one you are talking about), but the electronics that control the coil: the components that do the job of the points and advance mechanism in an old school system.

If it runs alright, then it's probably fine and neither you nor your friend should worry about it.

[Deleted User 62]

Cool, this happened over a year ago and he parked the bike in fear of doing more damage. The battery died in the interim and I am in the process of resurrecting it. New battery is at the Post Office, and it's frikking Columbus Day! (grumble mumble)

[Jean]

If it HAD been a problem, it would not have hurt to try to run the engine again after reseating or repairing the coil wire. If the electronics were damaged, restoration wouldn't have hurt anything. The loose wire probably still got a spark, but it was late as it had 2 gaps to jump...one at the coil and the other at the SP.
check wires terminals for corrosion and tightness and go for it.
PS. The gas is probably 'dead". and the carbs are gummy.

[Deleted User 62]

The loose wire probably still got a spark, but it was late as it had 2 gaps to jump...

I have to disagree with you there Jean, The way I understand it, electrons in = electrons out with no delay in that short a distance.

check wires terminals for corrosion and tightness and go for it.

I dug into the front cover today to turn the engine for valve adjustment, and found that the connector on the end of the wire coming from the bean can had disintegrated and possibly shorted to the engine case. The connector alone is not available from BMW, but the guy a MaxBMW said he knew of somebody who rebuilds them and has the connectors, but not how to get in touch with him. Anyone know him? He also recommended just filling the end with silicone and let it cure. That's what I've done. I'm also going to cover the join with heatshrink after it cures. Fingers crossed that the beancan isn't fried.

PS. The gas is probably 'dead". and the carbs are gummy.

No gas, one thing the owner did right is drain and flush the tank and carbs before storing it. They look super clean inside.

[Jean]

"I dug into the front cover today to turn the engine for valve adjustment, and found that the connector on the end of the wire coming from the bean can had disintegrated and possibly shorted to the engine case. The connector alone is not available from BMW, but the guy a MaxBMW said he knew of somebody who rebuilds them and has the connectors, but not how to get in touch with him. Anyone know him? He also recommended just filling the end with silicone and let it cure. That's what I've done. I'm also going to cover the join with heatshrink after it cures. Fingers crossed that the beancan isn't fried."

THIS is probably the biggest obstacle to overcome. Good luck.

You are entitled to your opinion about timing/spark gaps, but if you've ever watched a scope monitoring an ignition system, you would see there is a delay for each time the potential has to build-up to jump another gap. Of course, the higher the voltage that's available, the less time it takes.

[Deleted User 62]

Fingers crossed that the beancan isn't fried. "THIS is probably the biggest obstacle to overcome. Good luck."

The silicone has cured and I filled the float bowls with fuel to test the ignition. It started right up with no choke necessary, and settled into a nice, steady idle... whew! Now... on to the shifter seal and alternator brushes etc.

[Garnet]

Ain't it luverly when sumthin works out.