My NSR (again) came home on the back of a tow truck Saturday. Shortly after retrieving it from a tuner to get the jetting sorted, it started missing and backfiring really bad, going on one cylinder. I was afraid that trying to ride the 15 miles home with it backfiring would damage the motor so I had it towed. Just 2 weeks or so ago I had this happen, only then it was the top cylinder. I ended up replacing the coil to the top cylinder, after cleaning up the wiring harness connectors to both coils as best I could with emory board and contact cleaner. After replacing the top coil, the bike ran fine. This time it was the bottom cylinder that was off - plug was oil fouled, presumably because it had stopped firing.


So Sunday morning I put in a new plug, and thinking this might be heat related, i started it to see if it would run cleanly at start-up at least. Several immediate backfires later, the answer was clearly no. So then I looked at the front coil and found the coil blades showed evidence of arcing (2 parallel grooves etched in the blades from where the female connector i presume rubs on it, and the grooves themselves were blackened, with one or two pitted areas also visible). I swapped in a used spare coil I have, started the bike, and it ran clean - no miss or backfires. so then I put the suspect coil in to see if i could recreate the miss, and guess what, bike continued to run clean, no miss, no backfire! I'm admittedly working from deep ignorance in this area but WTF!

I don't know how long coils are supposed to last, but I'm thinking I have a problem that is causing the coils not to last as long as they should - i've probably been through 4 or so in the 3 years (and 10k miles) I've had the bike. It's always the same pattern of grooved coil blades becoming blackened - and I've several times tried to clean those connectors. I checked the VR and the readings suggest it is functioning. Powervalves appear not to be stuck. So I'm wondering which way to go. I suspect i could put in a new coil and the bike would run fine....for a while. But I'm wondering too if a faulty PGM could be intermittently causing the root problem (i was under the perhaps mistaken impression that once the PGM went, it went, rather than get hinkey intermittently). Or maybe i should invest in a brand new wiring loom, on the theory that the root problem is somehow in the connectors to the coils? BTW, in earlier coil episodes, i had crimped the female connectors tighter in an effort to make sure the blades were in tight (to avoid arcing from loose connection). Does the fact that I get these grooves on the coil blades mean it is now too tight - to the point where it can cause a problem?

Any help would be much appreciated - this bike has left me stranded more times than i can remember and it (like me) is getting real old. If i didn't like riding it so much when it is running it would long ago have been at the bottom of the ocean.
Sorry this is so long but I'm trying to give enough information for "you who know" to have something to go on.
Thanks,
JIm
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-Jim
'93 MC21