Hi all .I'm new to this NSR lark and have just got myself a 1988 MC18 and I am having problems with it cutting out after about 400-1600 yards then find I have no spark .I thought I had found the problem with one or two of the multi pin plugs as after I replaced them with bullet conections the bike fired up. Again it packed up and a push home was called for.I have tested out the coils ,loom,kill switch and ignition switch even the servo unit .I have just replaced the PCM box and it stopped again but this time I did get it to restart and rode it home.It starts first kick and goes like stink when it does go.Is it worth replacing the other ignition sort of box under the rear seat ?
Any ideas much appreciated as I would realy like to go more than a mile at a time.

Obvious maybe...But battery? are the plugs covered in oil did it all work before? Do you know if it ran beofre, Do you know it it previously siezed?
HT leads??? are the coil connectors clean and free from corossion?

Hi
Thanks for the input .I will check the battery with a load test but it does live on an optimate and that says its ok.The coil connectors are fine and as both the cylinders die it's possibly only somethig that is common to both like the cdi unit which I hope to replace with a used item soon or the pulse generator.I have yet to inspect this but think it would be unlikly to run fine then suddenly cut out only to start and run fine again.
I hope it is the cdi unit just breaking down after a few minutes use under load.If replacing it does sort it out I'll post the findings and we all might learn somthing as I have not had this problem in about 25 years of tinkering with bikes.
Thanks again
Alec

If it's an '88 MC18, there are two CDI units, one for each cylinder, so it's unlikey that.

Check the stator and the wiring from the stator to the fuse box and rectifier.

Also check the kill switch and the IGN switch. Try bypassing the IGN switch with a bridge to discount it. Check and clean all the connectors between these components.
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Andy.
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Thanks for the reply Andy.My 88 mc18 has one cdi box ( well I think it is ) that sits on top of the rear mud guard connected between the pcm box and the black box on the other side which i thought only did the valve servo control.I have tested and linked out the ignition switch and the kill switch.Most of the connections I have reterminated using bullets crimped and solderd just to be sure.I will take a look at the stator and regulator .Do you have any information on the resistances I should obtain from a good regulator/rectifier ?
I think I did test the three windings of the generator and did get same resistances but I will check again and write it all down in the morning again also test to ground.

are the battery connectors tight i had a very similar problem on one of my old bikes

Thanks Fenton ,I did check that they were greased and tight ,but it may be somthing simple like that.

You're right, I don't know what I was thinking!
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Andy.
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you were thinking MC16

Hi all.
I have had another tinker with the bike which runs fine in the garage ( over 15 mins ).I tested the generator windings and got a reading of over 350 Meg ohms to ground at a test voltage of 500v so that seems ok.I did test the voltage across the fully charged battery and got 14.4 volts with the engine running .This seemed to me a bit high but was steady at various revs ( I'm turning in to the neighbour from hell. ) Is this too high ,if it is , might it cause problems with the CDI boxes ?
Answers on a post card please...

14.5v is normal, if it goes over 15 you could have a problem, but if it stays steady you have no problem there.

I would start by finding the common wire between the two coils and work your way back to the ecu. I found I had a blackened ecu pin which caused a loss of spark not that long ago.

If both sparks are lost it can only be caused by this common wire or the ecu. If either pickup was duff the bike would still run on one cylinder as it would if either feed to a coil was also lost.
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If I have to take the carbs off once more...

Well ,I took a look at the pick ups ,cable conections ect all were ok had the bike running great in the garage so I tried it up thr road .Yet again it just stopped after about 0.4 mile.Pushed it home -won't restart.I'm now waiting for postie to bring me another CDI unit , just hope it is that !

I have just had a similar problem..

I reckon its fuel.

I changed over my coils,cdi's,rectifier etc and nowt changed...

Took of the carbs,thoroughly cleaned the jets,air screws,air holes etc and now its fine..

What I assumed was happening was..

When you start the bike its had time for the fuel to go down into the float chamber,when you run the bike it runs on the fuel in the chamber,chamber empties plus a little extra fuel thats trickled down,but theres not enough flow to keep bike going ?

my carbs looked immaculate before I cleaned them too...! , I cleaned the little holes with a strand of hair like thickness speaker wire.

Its a piece of cake whipping out the carbs and doing this,it wont do any harm to do it anyway.

hope you get it sorted .

I was thinking fuel starvation too, caused by the tank breather being blocked, apart from the fact you said there was no spark.

If there`s no spark, it does seem to point to something electrical breaking down under load, or when hot.