Had a coil failure, first real problem on my N15, but it seems resolved with replacement.

Went for a ride, me on Laverda 3C, son on N15. 15 mins in, the Norton sputtered and died. Got it running after a rest, checked fuel flow as best we could at the clear filter. Switched bikes, nursed it home, a bit of a pain; coasting and bump starting when I had to did the trick. I have had issues with bad fuel, but this seemed to be either fuel flow or coal heat soak. The bike has 2K miles on a Wassell Vape mini and dual-lead Tri-Spark 12V coil, and it has been flawless until now. I checked the flow & cleaned the carb. I recently put on a cutoff for sumping, so I checked its operation & wiring, and also the ignition switch, which was a bit suspect - I found a crack in the plastic on the back, and epoxy-welded it, and put on new crimps for the terminals. I also drained and replaced the fuel.

I tested the coil, but it's hard (for me anyway) to replicate heat soak on the bench. Ohms reading OK on primary, a bit higher than spec on secondary. I didn't want to throw a bunch of $ on a suspected problem, so I got a $30 3-ohm 'Magna' coil, which is a copy of a Dyna. All is good now, running beautifully. Maybe mounting the coil under the fuel tank overheated it? It's insulated as best I can from vibration with rubber, and never gave problems before. I moved the new coil an inch forward to hopefully cool it better. We'll see, but I'm happy that it's running again.

I've had several dozen bikes and cars, and the only other coil problem I had was a free Suzuki GS1100E that had some junk Chinese coils - it had the originals in the parts pile that came with it, and swapping fixed it right away. Seems that on my vehicles at least, coils live in hot places and survive just fine. Perhaps it's nothing to do with external heat? I can understand vibration, but my N15 isn't bad at all in that regard. Even considering that it's a Norton, it's sort of amazingly smooth the way it's set up. C'est la vie.