Any ideas on what the problem might be?

[bigfootpete]

My mate has had his bike in the shop for two months and they couldn't sort out the problem - so hoping that someone has suggestions as to what the issue might be
from the experts here (Mike!  [size=78%])[/size]

The HT coil no 1 burns out -  he has blown 2 of them, same one each time.
The bike is a z750 2007/8  model, spark plugs have been replaced bike has done 31,000miles.


Anyone got an idea? or are more details needed?

[Fazerider]

A faulty CDI unit sounds the most likely cause, tricky to diagnose without an oscilloscope (not a common item in bike workshops) or a known good one to swap it with.
Alternatively, if the HT leads from it to the plugs have broken down that would result in higher voltages in the coil which will result the windings arcing. Were the leads re-used or are they integral to the coil?

[bigfootpete]

I think he bought new leads as well... I'll double check.

[rustyrider]

Genuine coils or eBay cheapo pattern ones?  He could have been unlucky having the first one go but if it was then replaced with a poor quality pattern one and that failed too it suggests a problme elsewhere which it isn't. 

[bigfootpete]

Ha, he's actually one of the most computer illiterate people I know! So that rules e-bay out - he probably paid full stealer price for it.


I'll ask him some more questions when I meet up tomorrow at Box-hill (if he can make it  :b [size=78%]).[/size]

[BIG MAC]

Poor earthing - resistance in the plug cap - breakdown in the LT side - Changed coils but is he retaining the same control pack if there is one?

[bigfootpete]

Ok, caught up with him this afternoon - he got an offer to sell for £2k so has decided to take that offer rather than try and sort it himself(and worry if something else is going to go wrong) - but I shall also mention your comment BM.

Thanks all for the replies!

[griff86]

I know this problem has been sorted.


I've seen this on a few bikes the past year and all kawasaki. I would agree with Fazer rider thats it was a faulty cdi, I've had the same problems with bikes coming in with a blown coil, it was from the rectifier failing causing the battery to overcharge which created a knock on affect from there blowing the cdi, coil and sometimes the rev counter.


If I had a kawasaki I'd run a volt meter on the bars to check battery voltage as I don't trust their rectifiers.

[BIG MAC]

Not sure a rectifier would 'pick on' the same coil...or even the same coil pack...presumably there is a combined rectifier regulator however while this may affect charging..ususually to the detriment of the battery? not sure how it would affect the low tension circuit in such a way as to fry a coil whereas a poor earth may cause back earthing through a more expedient route? electrics definitely not my forte and probably some schoolboy errors there but I think the principles are ok

[griff86]

From what I remember is that coils work from a pulse from the cdi and when the rectifier goes it can't regulate the power from the alternator which then over charges the battery which sends to many volts through the wiring and blows a certain zenner diode inside the cdi which on the bike I was working on had actually cracked the coil and blew the rev counter as that wasn't cable operated with the over charge. Common on ER500's.

Each time I've seen this it blew one of the coils. Changed the coil and no spark, changed the cdi with a known good one and then had a spark. Ran the bike for second after the fix to see that the battery was showing 15v plus, changed the rectifier and voltage was back down to where it should of been.

Seen this a few times now, would always check this first, spent so many hours head scratching with wiring, its starting to make sense slowly.

[BIG MAC]

But would a badlt earthed coil fry a CDI? as distinct from the other way about?...or possibly even a bad engine earth..questions questions

[Fazerider]

I think you're probably spot on with that diagnosis Griff.
It's certainly well worth checking the battery voltage is being regulated before installing a new CDI.

I've not been impressed by the electrics on the two Kawasakis I've had. Quite apart from the poor quality wire they used, both suffered ignition problems:
The GPZ305 used a magneto to provide a high voltage to the CDI: this coil packed up after a few years... I got the generator rewound by an incompetent company called Electrex as I couldn't afford a new one. Even once they'd got it right that coil gave up after a few thousand miles. Eventually I built a small circuit to generate the 130V pulses needed which ran for the rest of the bike's life.
My GPZ500 started having intermittent ignition problems when it was still under warranty: high rpm would provoke it, but not if the engineer from the dealer was riding it... I ended up having to diagnose it myself. After checking the CDI itself was OK (by making a variable pulse generator to simulate the pick-up pulses) I found it was the pick-up coils themselves producing such a high voltage at high revs that it was overloading the input to the CDI. Some back-to-back zener diodes solved the problem.