NSR125 ignition

[Tony Norton]

Had a call from my Grandson "....my bikes conked out and won't restart....". Why call me, because I have garage space, loads of tools, and he and I between us have rebuilt practically every bit of the bike, barrel, piston, clutch, brakes, forks, chain set etc etc.

The bike is, I believe, a "grey" Italian import NSR125FP. This, I am told, is established by the frame number which is ZDCJC22.... but here it is a little strange because it is followed by not an A, B, C or E, but by 900F and a 6 figure frame number. It is definitely unrestricted mechanically as the lad has, so he says, "maxed out" at 13K.

When it packed up on him he said that the engine dying was simultaneous with the tacho dropping to zero. This happened a few times before it gave up altogether. These observations led me to believe that it was either the output from the CDI unit to the coil, or the coil itself breaking down. I did, at first, get a weak spark but now am getting nothing.

The RCU is a TV-78 and the CDI unit is marked only with KBS and what I assume to be a serial number "2.3 121". It appears that numbers may have been scratched off!

The resistance readings of the coil are: - Primary 0.6 ohms, Secondary (without the 5K ohm plug cap) 3K ohms (where do I find an omega symbol on a UK keyboard?) Does anybody know what the pulse level should be at the coil? With a digital meter set to AC I am getting about 6 volts between the terminals that connect to the coil. Is it possible to check the output from the CDI unit? The resistance reading of the pulse generator is, according to a downloaded manual (which doesn't exactly match this model) within spec. All tests have been done with a healthy slave battery connected, not the mini battery fitted to the bike.

From what I read on this site "Alains" is the man with the knowhow. Hopefully you may have a little time spare to help me Alain. I am somewhat a loss

Thanks in advance for any help I receive.

Best Regards

Tony Norton

[biker_king]

hi, im striping my bike today so will be able to test the coil and give you the readings that i have.james.

[Tony Norton]

Thanks James,

Tony N

[alains]

the ignition is an AC-CDI . the coil in the stator produce around 200VAC in order to charge the capacity (1,5 µF 400V) of the CDI . when the ignition works it's quit impossible to test the courant going to the coil . your model is a NSR125F , which is the model unfaired . a little difference in the alternator : your bike has a one phase system instead of the NSR125R which has a 3 phase system but the ignition which is separated inside the stator is exactly the same . here is the wiring picture :
https://www.geneva-racing.com/~alains/schema_F.jpg
about ignition bugs , they come mostly from loose contact on the black/yellow especially on the CDI connector . in my file https://www.geneva-racing.com/~alains/NSRtips.doc you've got a complete search of ignition bugs
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[Tony Norton]

Hello Alain,

thanks for your response. You may be interested to read Tonton's reply on the Geneva-racing forum.

I think a continuity check on wiring, now I have schematic, for which I thank you, before I start on more voltage checks. Will let you know, via Geneva-racing, how it goes.

Merci encore

Tony Norton

[Tony Norton]

Hello again Alain,

As I said before, I am puzzled by the frame number of Sam's bike.

You are not the first person to say it is an NSR125F, although most others have said NSR125FP. It certainly looks like an "R", full fairings and "fox-eye" headlights, and the wiring doesn't match the NSR125F schematic you pointed me to. It does, however, match the NSR125R schematic drawn from the same source, a 3 phase alternator with 3 yellow wires + Gnd on the connector, a single Red/Black wire and a pair from the pulse generator.

The resistance of the stator was out of range though at 68 ohms, probably something to do with the water in there, although this has risen to 77 ohms after 4 hours in a dry room.

I have printed off your NSRtips document for future use.

Best Regards

Tony Norton