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

good luck. mine did the same,would go down on one then start missing/back fireing then come back on.it was a broken thrust washer.hope yours is a simple problem.

sorry to hear bout your troubles. Im in the process of freshing up my motor a bit due to poor starting. pipes are all spooged up also. i have a spare pgm you can try out to see if that changes anything. my bike wont be runnin for a bit. plan on sending my cylinders out to eric gorr to get replated. ive been learning the hard way for a while now. call me at the shop 619-474-2025.
john

Jim,

I will see if I can decipher some of the Workshop Manual information this evening to help you out.

I don't think you have done anything wrong at all. Certainly, tightening the connections previously won't have harmed the contacts, only made them harder to pull apart! Pitting and blackening of the contacts would normally suggest loose fittings/arcing though, at that could cause a resistance to build up. Have you checked the regulator/rectifier, and the output from the charging system. If the voltage is too high (should be around 14.2v - no spikes when revved) or too low, this can cause major problems.

If the worst comes to the worst, I'll at least e-mail you scans from the Manual.

It's curious that swapping out the coil fixed the problem, then swapping back showed no difference. This would lead me to assume that it's not a necessarily a coil fault; maybe a pick-up coil or the stator instead. I had a stator failure once, but it stuttered on load and at high RPM. There is something in the manual about all this though... I'll get on it tonight.

If you need a new harness, I think I have one. In the mean time, see if you can try John's PGM!

Andy.
NSR-WORLD.COM

Hey thanks for the offer John! I actually do have a spare PGM available to swap - I've just been trying to make sure first I wouldn't fry it in doing a test (and this thing is so intermittent I don't think I would know if it made the difference right away, unless maybe i started from a miss baseline). Andy, I did check the VR using the Electrex guide....it said there should be "greater than 13.5 V at 2500 rpm" and to then take it to 5000RPM whereupon it should read 14.8 or less. Well, at 2500 I was getting 14.9, which is above 13.5 but is it too far above? Guide did not give an upper range for 2500RPM. When I took it to 5000RPM, it registered 14.2 - 14.5v, which seems normal. So if the 14.9 was not too high at 2500 RPM, then it meets the criteria for 'charging sysyem ok" - this is an Electrex VR I have in the bike, not stocker, BTW. So is the 14.9 at 2500 RPM too high?

I think I may first try replacing the female connectors to the coil, on the theory that there is something hinkey there that can cause an otherwise sound coil to misfire some of the time (as when it misfires, is taken out briefly, and then is reconnected and works!). Maybe fanciful on my part, but it costs less than a new wiring harness to try. Andy, please hold on to that harness though, and ANY info you guys can send my way is very appreciated.
Thanks,
Jim
_________________
-Jim
'93 MC21

Sounds like you have an intermittant wiring fault there. Might be worth doing a continuity check along the wires and having a good 'wiggle' to check for breaks. Also do one from the wires to the chassis to find any chafing that may have happened over the years.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Hi Guys,

quick update and question:I replaced the female coil connectors on the wiring loom. Top and bottom both showed evidence of arcing, which is no surprise given the state of some of the coils I've replaced. I ran the bike about 20 miles around the 'hood with no signs of a miss, which proves......nothing, given how intermittent this problem has been.

Here's my immediate question: when the bike goes on one cylinder, and is doing that dreaded puh-puh sound with the occasional backfire thrown in for drama, and I'm, say, 15 miles from home, will it harm the engine to limp the bike home in that condition? Last time I called a tow truck, but that is getting expensive and the wife totalled my pick-up truck, so I need to plan ahead.

I'm thinking maybe I'll just set up a circuit around the house so that I am always within pushing distance. Thanks.
-Jim
_________________
-Jim
'93 MC21

As you have a nsr i thought that being a member of the AA(i think its the triple A in your neck of the woods)is a must,no more recovery bills.

I doubt it'll do any damage, it'll just run like a 125!
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Jim,

I'm still looking through the Workshop Manual for something that may be of help to you. I'm sure there is a trouble-shooter I can translate/get translated, but it's not easy to make the electronics stuff out, and a lot of it calls for a special Honda/Showa meter!

Silly question, but have you traced the coil wires back to the PGM to make sure there are no bad connections or any wires with cracked/broken insulation?

Andy.
NSR-WORLD.COM

Having been to San D before, I love it (Gas Lamp quater rocks!), and am quite happy to come fix your bike if you can pay the airfare. And put me up. And ply me with beer. And classy women. In fact, I made some aquaintences last year...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Jim, I'll better that deal...

Airfare, beer, a place in the garage next to the NSR, and cheap sleazy women will do me! (In that order is fine too!!)

Andy.
NSR-WORLD.COM

shoot. i can hook you up with some sleazy pacific beach girls. San Diego is full of premiscuous women. they dig on guys with thick accents, eh.

you can sleep in one of the rooms above the shop if you dont mind nesting with old cb parts.

The way this has been going, it might well be cheaper to fly both of you out here in the off-season! I can source beer and John apparently can source the sleazy women - classy women may take a bit more research...being married and waaay out of the loop, I would have to rely on others for that too.

Andy, the wiring diagram seems to indicate it is a continuous wire from the PGM to coils (no connectors). It disappears into the wiring loom and then isn't seen again until the other (coil) end. No obvious cracked insulation where i can see the wire anyway. Consensus seems to be I won't damage the bike if I limp it home on one cylinder, so I'll probably go ahead and see what happens with the new female coil connectors - probably just won't venture too far....will be watching the airfares too.
Thanks for the help.
-Jim
_________________
-Jim
'93 MC21

Seen this problem on several NSR's and it's always been related to the dodgy connectors that fit to the coils. It also happened to my 300 which was an instant disaster obviously. Anyway, I just snipped off the connectors, fitted new ones and it's been running fine ever since.