Destroyed both coils...

[Northern Mike]

The bike is a 1979 gs-750e.
It sat for a year in storage. Brought it home, peiced it back together, new fuel, and she fired up no issues. Ran about half a tank of fuel through it in the garage over the past couple of weeks. Went to fire it up last night, got a loud backfire, and nothing. Left it until this morning when I noticed the left coil split apart and leaked. Notice later, the right one cracked in half. These weren't broken last week when I was working on it.
Before I find new coils and they split, what would have caused this?20171221_171722.jpg

[Steve]

Usually, there are only two things that will damage a coil: impact and heat.

Impact will happen only if the tank is off and something hits the coils. Apparently that has not happened.

Heat can happen if there is too much current going through the coils and there is no moving air to carry it away. That might have happened. It takes quite a while to run half a tank of fuel through a bike without it moving, my guess would be several hours. My reasoning is this: at speed, you will go 150-175 miles per tank. That will take about three hours. At idle, you won't get any miles per tank, but you will be using it at a slower rate, so it will take longer than three hours to drain the tank. Half a tank could easily be 2-3 hours. If you did not have a fan blowing across the engine, no telling what might have happened there, but you also need to assure that there is moving under the fuel tank (if it is in place) to assure that the coils are cooled, too. How long did it run at any one time?

Also, you state that you brought it home and pieced it together. Were you the one that had the bike and rode it before it was taken apart? In other words, how much of the history of this bike do you know?

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[Northern Mike]

Thank you for the reply.
It probably wasn't a half tank, probably less. Run time would have been tops 10 minutes at a time. The garage is at or just below freezing.

As for piecing it back together, it was myself that pulled it apart. Was stored at a friend's shop about an hour and a half drive away as I didn't have a garage at the time. Drove the bike there, ran it's best it had ever ran.
I'm just concerned it could be something that wiped both out. Bike started with 3 kicks after sitting a year, then these go.

[steve murdoch]

Any chance you left the ignition switch on for an extended period? Overnight?
Any chance one of the times you were starting it the bike was hooked to a car battery or a running car?

[GregT]

Has the bike still got points ignition ?
If it's had over the top voltage - which is what it looks like - an electronic ignition would have failed before the coils in my experience.
Points on the other hand can carry a lot more voltage...

Usually, if the ignition has been left on, only the coil or trigger which is energised will burn out.

[Big T]

It has Martek coils, does it have a Martek ignition?

[Northern Mike]

Any chance you left the ignition switch on for an extended period? Overnight?
Any chance one of the times you were starting it the bike was hooked to a car battery or a running car?

I think you nailed it. I was working on a new aftermarket tach/speedo with a toasted battery. Was using a car charger to top the battery up enough to run the tach. Lessons learned...

As for the ignition itself, I believe they are still points. I tried location info on these coils that came one that bike a year or so ago (forum thread around this forum somewhere, with no success.
Being an aftermarket coil set on potentially stock points, any suggestions on replacement coils?

[Boriqua]

I think my
3ohm dynatek coils were about $120 with new wires and caps. Trouble free so far.Ebay has dynatek looking coils for much less but they are Chinese knockoffs. However if cost is a real concern they do seem to come with a warranty and when I was doing my research here it seemed several people had used them and were happy.