N2 wont rev over about 2500, just dies, seems electrical?

[JonW]

Ive asked this on the RDRZ500 forum as well as the owner of this bike frequents that site, but not everyone from here goes there, so ive posted it here for ideas, Im stumped

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Ok, this isnt my bike, its local boy James'... I know everyone says bikes with issues are not theirs, but really this time its not mine... :smt016

Japanese N2 250.... started having an issue about 6months back that when riding it would die and immediately come back at about 8000 revs, when it did it looked like the tach died as did the rest of the electrics running the motor, as it felt like the whole bike died. Seemed to clear itself and then a few thousand kms later it did it again, cleared itself and was ok again for a bit, and repeat... but it got worse to the extent that it just kept dying and finally gave up the ghost only 100m from my house with what looked like no spark. We did manage to get a spark on occasion but it was weak and small.

We cleaned the plugs and some connections and it worked again enough to get him home 10km from my house, but it was a horrible ride up there with it dying and coming back. he found that flipping the kill switch seemed to allow it to fire back up (the bike was doing 100kph at the time so the motor fired back up as it was being spun by the back wheel etc).

At his house we found the loom was a mess, the coil lead connections were dirty and a bunch of other things, and he started a clean up and repaired the loom, but nothing seemed to fix the issue...

he tried:

- swapped the CDI for another one - its a 3HM, anyone know issues with those?
- bought a brand new OEM coil incl leads ($$$)
- fitted new caps
- changed the plugs

Still did it, but now it started and seemed to sound crisper, as all those things improved the spark of course.

Then he got another stator and swapped that and now it dies at about 2500... oops... we felt he was making progress as thats the first thing he did that had any effect, even tho it was worse.

He then fitted another loom as we felt it was connection related and his old one was really horrible... it wasnt an exact match but it was close... he set about making it work and isolating things and just using the simplest of circuits.

Now the kill switch and ignition are NOT attached so we know its not them.

Still does it... sigh...

Bike starts on the button now, but even on fast idle you can hear it reach about 2500 and then cut and come back, its like a rev limiter... weird.

I dropped up there today and we pulled the flywheel off again and I could see the crank and the flywheel had rust on the tapers. we cleaned that up and put it back on. I really thought we might have found the problem with this, it was really gross. but no.... Grrrr! :smt013

Since we had a quick before n after we could tell the bike is sprightlier again, and maybe a little better but it still does it... idle, cut, idle, cut etc.... totally unrideable as it cuts totally dead on even the faintest of throttle.

So... with most things replaced now and a lot of $$ spent, hes thinking of having his stator rewound and buying another flywheel as hes been told they go bad... tho ive never heard of that, its a bunch of magnets... can it really go bad?

Does anyone have any ideas? Is there any kind of stator test he can do to prove the ones he has are duff?

And... in full Sherlock Holmes mode, (once youve excluded the obvious, the bizarre may well be the answer etc) Could this even be unrelated to the electrical system and actually be carbs?

I dont often shrug and think, 'thank fek this one isnt mine...' but wow, its a tough one... thank fek it isnt mine! :smt037

(hopefully James will add to this, as maybe Ive forgotten some of the things hes done...)

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Cheers guys!

[muttsnuts]

its probably the pick up or the high/low coils breaking down on the stator, is it worse when its hotter ?

[midlifecrisisrd]

As mutts says

I would try another flywheel if you can. Weak magnet on the pick up would cause problems

Steve

[muddyfox]

might be worth lapping the flywheel to the crank as well,mine worked its self loose over a few 100 miles and gave me a weird issue

grinding paste, beer, wait till you see the paste turn grey, dont forget some locktight!

[JonW]

Jan 22, 2015 13:52:51 GMT 1 muttsnuts said:

its probably the pick up or the high/low coils breaking down on the stator, is it worse when its hotter ?

I think it is worse when its hotter, but the first time it happened the bike had just been started on my driveway and had been sat idle for an hour or two.

I would agree on the stator, but weve swapped it, were we just unlucky?

[muttsnuts]

Jon, I reckon you might have been unlucky, best way to test the coils and pick is to test them cold and then using a hair dryer or hot air gun (paint stripper type thing) gently warm them up and see what the readings do, if they go out of tolerance then they are knackered, from the sounds of it, they are knackered anyway

HTH

[JonW]

Jan 22, 2015 14:28:10 GMT 1 midlifecrisisrd said:

As mutts says

I would try another flywheel if you can. Weak magnet on the pick up would cause problems

Steve

Steve, Interesting you say that as someone locally suggested the flywheel but my way of thinking was 'do the magnets really fail?'. Ive never had a bad one and really its a 'works or not part' I thought as it has no moving parts etc. But I trust ya, Ive just never seen tat as an issue and wonder why it worked so intermittently for months?

[JonW]

Jan 22, 2015 15:43:21 GMT 1 muddyfox said:

might be worth lapping the flywheel to the crank as well,mine worked its self loose over a few 100 miles and gave me a weird issue

grinding paste, beer, wait till you see the paste turn grey, dont forget some locktight!

That's James' next job. I now lap all my flywheels, as I had some really nasty arcing on my LC421 that ate chunks out of my crank making the flywheel almost impossible to remove as it was basically welded on.

[JonW]

Jan 22, 2015 22:11:06 GMT 1 muttsnuts said:

Jon, I reckon you might have been unlucky, best way to test the coils and pick is to test them cold and then using a hair dryer or hot air gun (paint stripper type thing) gently warm them up and see what the readings do, if they go out of tolerance then they are knackered, from the sounds of it, they are knackered anyway

HTH

Thanks mate, will direct James here so he can read this, I just didnt want him to get all excited about spending another $200 on sending a stator to be rewound and then finding that wasnt really the issue as everyone suggested it was something else.

[bigkenx]

I agree with the advice you've had , I have had a flywheel lose its magnitisium the back run really intermittent and had a problem with a stator where the bike wouldn't kick start but would bump and run very head melting, and always try to stay right minded as just because it's new doesn't mean it's ok always try to replace one thing at a time and I always put the old one back on so I'm not making a massive puzzle for myself and chasing my tail ive had brand new spark plugs and had a problem and checked everything but kept saying to myself can't be the spark plugs there new , turns out spark plugs are f**ked

[higgsy]

Jon that sounds stator based to me. The flywheels do pack up, had it before on a TZR, took me ages to suss it. It sounds as if the higher output isn't working or is intermittent. It's always a process of elimination and that can be bloody frustrating. I'd swop the flywheel and see what happens i think. If it's possible to swop for known good parts that's always a bonus

[JonW]

Thanks for the input guys, hopefully the owner will post on here and let us know how he is going...

[okeydokey]

Is it a jap import? Restricted? Some of the restrictions we're in the clocks. Don't know all the details just that you mentioned it sounding like a rev limiter. Might be worth a bit of further investigation.

EDIT: Actually on an N2 that may not apply thinking about it. Was just a thought thats all

[rz250rjapspec]

Thanks for all the input peoples, I'm in the process of having stator rewound. At small coil rewinds nth Geelong in Victoria. Also now noticing some deformation on flywheel, looking like some magnets may have corrosion and are expanding so will try to find another. Thanks James.

[4l04ever]

I would get some of those spark plug testing/diagnostic caps which flash when you have a spark. You can see if the spark is stopping when you rev the bike up.

www.ebay.co.uk/sch/i.html?_odkw=spark+plug+diagnostic+caps&_sop=15&_from=R40|R40&_osacat=422&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xspark+plug+diagnostic&_nkw=spark+plug+diagnostic&_sacat=422

If the spark is fine, you are barking up the wrong tree......

If the spark is failing, you need to track back through coil/CDI/pickup etc.

[JonW]

The bike defo dies when you rev it up, it will idle and then as you let it come up (slow or fast) it will reach a point and the just cut out, once the revs drop it all comes back online. Its sort of like a rev limiter in that respect, if it dies at really low revs then it stops and is hard to restart, but that seems to happen less often, mostly it was doing the 'rev limiter' thing.

[Deleted]

jon

I have one of those spark testers, I can send it to you if you wish

[JonW]

Thanks Howard, its James that has the problem tho, he was just to lazy busy to post the thread up...

[rz250rjapspec]

Massive Thankyou to jon for very large effort in helping with the very annoying n2 issue.
Now happy to report bike is running very well. After 110 KMS last night, the bike did everything I asked of it.
It was the stator, hi low or exciter coils.
After rewind the issue is gone. Flywheel is running ok.
Thanks to all and I will post up photos someday soon.
Thanks James.

[JonW]

phew, glad its fixed and running well again, Enjoy it James!