Oscillating idle.

Posted this on Z1oc but not had any responses so throwing out there to a wider knowledge base. 
Having trouble trying to pin down and remedy the cause of an oscillating idle issue.
Firstly it should be said its a mix mash of parts build. Z1000J2 with gpz1100 top end. Vm 26 SS bored to 29.5mm. Runs perfectly for low down grunt with stock 900 a4 jets and needle. Great plug colour. Colour tuned to good colour. Stock J ignition/ignitor/coils. Kill switch and stand override switch work perfectly with no drop of power to the coils. 
Symptoms, at idle the rpm oscillates from 1k to 1.2k and back again over a period of 5 seconds climbing up then 5 seconds descending down and just continually repeats. It not erratic its consistent.
It's not the end of the world annoying just a little irksome that I can't dial it out.
Kinda thinking because of its consistency it's electrical supply to the coils but not yet checked to see if voltage oscillates with revs and if it does suspect ignitor? 
Open to other ideas before getting back at it tomorrow.

Warren I would be surprised if coil voltage fluctuations would cause this, the coils are working at approx 9.5v during starting so the fluctuation would need to be significant and I would expect it to present as a miss-fire under load rather than an idle issue.
As you are running velocity stacks can you see if the slides are moving causing the increase in idle (there is a lot of detail around the machining Rob (Zed1015) did when he bored the carbs on his BOTM -  details are in the Z1OC link to his build thread which is in the feature)
Have you tried a strobe light to see if ignition advance is fluctuating causing the idle issue ? - (increased advance will increase idle speed)

Hi Guy, my carb bore was pretty much identical to Robs write up. It does have stacks but the rise n fall in revs occurs even without a throttle cable fitted. It did it when I bare bones tested the motor on the bench. At that point I thought a final carb setup and general tune once the bike was built would eliminate it, but no. 
I'm kinda thinking it's so rhythmic that it's not mechanical like slides lifting. Almost like the ignitor is pulsing but the finer details of electrickery is not something I fully understand. I'm not entirely sure of the function of the ignitor as the bike has mechanical advancer and electronic pick ups, much like Dyna, so what's the ignitors function? and could it fail in this way and if it did would it cause similar symptoms? 
Timing has been strobe and it is fine with no fluttering. 

As I said, it's not a major issue but just something it would be nice to resolve as my curiosity is now piqued.


 

You could only check the output from the igniter with an oscilloscope. I have one that I don't know if I am going to use get (wiring is a bit brittle) but happy to send it down to you as a test piece rather than buying one (they are £80 and upwards for a used part !!) you can then return and source a replacement if that is the problem. There is a UK company that do one for around £240 that has an optimised map

Kawasaki Z1000 Z1100 KZ1000 KZ1100 CDI IC IGNITER (21119-1030 1041 1356) [CARI-KA-Z1000-21119-1030-1041-1356 Kawasaki KZ1000 KZ1100 CDI] - £245.00 : Carmo Electronics, The place for parts or electronics for your Motorbike Quad Scooter Car or Jetski

Are the carbs vacuum synced?

Nessism wrote:

Are the carbs vacuum synced?

They are but won't hurt to double check.


Guy, it's not that big enough of an issue to go that much trouble, but thanks for the offer. 
 

Warren3200gt wrote:

Posted this on Z1oc but not had any responses so throwing out there to a wider knowledge base. 

 

I am giving this some thought and wasn't going to post a reply until i had a solid reasoning for the cause.
I've never had this issue myself and all the carbs i've bored have worked perfectly with no problems.
With the rise and fall being consistent it has to be either a repetetive electrical surge or a metered air or fuel issue.
Fatter spark allowing fuller combustion and an inconsistant air leak or fuel surge will all cause the rise and fall.
Something like a leaking o'ring on a needle jet tube or similar which weeps enough fuel to raise the revs but then can't maintain the feed once the revs rise so the revs then drop and the cycle repeats is one possibility.

Hi Rob, I was hoping you might chime in  ​​​​​​.
It certainly is an odd one and something I've not encountered before either. 
When I did the carb bore I replaced all the consumables as you would expect. 
I'm definately leaning towards an electrical cause and was thinking along the spark fluctuating in performance lines as you mentioned aswell. 
Can you explain in laymans terms what the ignitor is supposed to do? 

The ignitor takes a low voltage signal from the pickups to trigger the primary voltage to the coils.
On machines with no mechanical advance they also electronicaly advance and retard.
My electronics knowledge as regards to diodes and resistors ect is limited to near zero so won't be of much help with it's internal gubbins..




 

Warren3200gt wrote:

Hi Rob, I was hoping you might chime in 

​​​​​​.
It certainly is an odd one and something I've not encountered before either. 
When I did the carb bore I replaced all the consumables as you would expect. 
I'm definately leaning towards an electrical cause and was thinking along the spark fluctuating in performance lines as you mentioned aswell. 
Can you explain in laymans terms what the ignitor is supposed to do? 

To all intent and purpose the igniter is a complicated "relay" however looking at the replacement unit on the website I posted it appears there is also some degree of "ignition curve" control also (varying delay between the trigger pulse and firing the coil) The igniter also controls "dwell" as too much dwell would overheat the coils (on a 4 cylinder car the dwell is typically 50 degrees so 50x4 would be 200 degrees. Therefore for each firing cycle the points would be open for 40 degrees (4x40 + 4x50) this is why 2 strokes had a set of points for each cylinder (with double the firing cycles the dwell would be too short to fully charge the coils with a single set of points) with dual pick ups the dwell would be approx 160 degrees between trigger pulses so a total of 320 degrees per rotation which may burn the coils.

So just a step towards complicating things that  can fail and not be fixed, just replaced. Originally I was almost tempted to replace the whole ignition system with straight forward Dyna stuff and deleting it but It seems to work fine apart from this idle issue, which it might not be causing, 

It's only my ocd that even prompted me posting 

see edit ref "dwell" control