Montesa Cota 315R - no spark issue

[b40rt]

7 hours ago, scifi said:

Quote,,,,   Measured peak voltage raises until about 3rd or 4th kick and then stays around 20V. Voltage raising is presumably due to capacitor charging in peak voltage adapter.
While taking measurements all loads were disconnected (in this case CDI).

I think this points to the problem.  You are charging the CDI Capacitor, but the CDI is not discharging it to make a spark.  Probably the CDI discharge transistor (or Thyrister.) has gone open circuit.

.

Agreed.  Think I said that several posts ago, but apparently it's not a complicated enough answer.  This post, and answers, demonstrate the real problem with trials.......

[lineaway]

You did at that, but a running bike put away for 1.5 years should not have nothing to do with the CDI. It should be a grounding or connection issue. But we all know stranger things have happened.

 

[Trialeovince]

On 7/12/2019 at 8:54 PM, konrad said:

When kicking, can you correlate a spark/no spark event with a difference in the peak output of your exciter coil?

No difference in peak output voltage of exiter coil between spark/no spark event spoted.
Only thing noted was that spark appears when kickstarter is already returned to starting position and not while actual kick. As if spark came with a delay.

On 7/12/2019 at 9:27 PM, lineaway said:

So, yes trim the wire. Check the bolts. Does the stator have a ground wire? Not usually, it runs through the engine to the frame. Chances are all those bolts are chalk white on the threads. 

Spark plug cap wire trimmed - no difference, no spark.
Stator taken off the flywheel cover. Corrosion was present as predicted. Seat on flywheel cover, metallic part of the stator and bolts were cleaned using wire brush on rotary tool - no difference, no spark.
Stator does not have a ground wire.

On 7/13/2019 at 3:47 AM, cascadeimp1 said:

What is the ohms range given in the manual and what does your exciter coil read?

Exciter coil (10,8-13,2 Ohm/25°C): actual value 12,6 Ohm/19°C

Other coils:
- primary ignition coil (0,45-0,55 Ohm): 0,6 Ohm
- secondary ignition coil with plug cap (12,4-16,8 kOhm): 14,6 kOhm
- secondary ignition coil without plug cap (8,6-10,6 kOhm): 9,7 kOhm
- charging coil (0,64-0,79 Ohm): 0,8 Ohm
- pulse generator (90-110 Ohm): 120 Ohm

On 7/13/2019 at 8:55 AM, b40rt said:

Can you swap the cdi for a known good one ? Sounds like a failing capacitor.

This thread is about one of two 315Rs that were known to be imported and sold new in our country. So chances to swap the CDI for a known good one are... lets say limited.
This is why I would be very grateful if another user of 315 would take a measurement of exciter coil and pulse generator peak voltage. If those are somewhere near values I have measured then CDI is probably cause of the problem. But I would not like to buy a new CDI only to get to know that it is actually stator that is causing problem. And vice versa.

On 7/13/2019 at 12:53 PM, konrad said:

And, at what temperature is it being measured?

Mentioned above - 19°C.

On 7/13/2019 at 12:53 PM, konrad said:

You should see the coil's resistance increase gradually as you heat it.  If, however, the resistance drops suddenly, this indicates a problem.

Coils heated with fan producing heat of approximately 170°C.
As coils were heated, resistance slowly increased from 12,6 Ohm to 14,2 Ohm. Then heating was stopped.

On 7/13/2019 at 1:15 PM, konrad said:

That makes a compelling reason to buy or build a peak detector.

Peak voltage adapter used to measure stated values was built according to this link, but using smaller capacitor (4,7uF).

On 7/13/2019 at 5:40 PM, johnny_rotten_dab said:

Hi, if i were to fault this, i would begin looking a wiring diagram and what basic components are required to start it...........remove stop button wiring plug from icm......remove mini plug to rectifier.....check if any wiring either side if coil is to ground(Bu/W)...check that joint @  BU/W  and also the pulse ignition plug/joint(R)...check joint to primary ignition side(GR)...and check G from icm to ground, dont use a multimeter use a 12/6v battery and bulb tester to drive current through wiring i.e. a load....when your happy with all this then kick it over and see if you get a spark......if not....start  to measure the pulse(with a cheap portable scope with a 10:1 probe)...and then ......etc...if you have a funtiongen you could replicate the pulse into the icm....goodluck

This is what has been done before.
- stop button removed - no difference
- rectifier unpluged - no difference
- non of the wiring on coils is connected to ground
- all wires connected to CDI unit checked for continuity - all OK
- all joints cleaned with contact claner although none were visuably corroded

Unfortunately I do not possess scope or function generator to replicate pulse.

On 7/14/2019 at 1:14 PM, scifi said:

I think this points to the problem.  You are charging the CDI Capacitor, but the CDI is not discharging it to make a spark.  Probably the CDI discharge transistor (or Thyrister.) has gone open circuit..

I am suspecting CDI from beginning, but as mentioned above - before I order new one I would like to know that voltage values from stator coils are OK for this particular model.

On 7/14/2019 at 9:07 PM, lineaway said:

You did at that, but a running bike put away for 1.5 years should not have nothing to do with the CDI.

Exactly my thoughts.

Edited July 15, 2019 by Trialeovince

[konrad]

3 hours ago, Trialeovince said:

Exciter coil (10,8-13,2 Ohm/25°C): actual value 12,6 Ohm/19°C

As coils were heated, resistance slowly increased from 12,6 Ohm to 14,2 Ohm.

Compliments on your testing and reporting skills!

That resistance indicates a fairly robust wire diameter that would be less likely to fail than a much finer wire.  The results you saw when heating the coil also indicate it is not likely to be the problem.  You would need special test equipment and "ring" the coil in order to test for a few shorted turns.

cascade1imp quoted a reading of 20 - 30 VAC (no peak reading adapter) on the exciter coil when kicking. (Was this with the CDI connected, or not?)   If no one is willing to build your peak reading adapter (with a 4.7 uF capacitor) and test their bike, this may be the best information you will get.

Edited July 15, 2019 by konrad
typo

[Trialeovince]

On 7/15/2019 at 10:04 PM, konrad said:

That resistance indicates a fairly robust wire diameter that would be less likely to fail than a much finer wire.

Indeed it is bigger in diameter than suspected.

On 7/15/2019 at 10:04 PM, konrad said:

cascade1imp quoted a reading of 20 - 30 VAC (no peak reading adapter) on the exciter coil when kicking. (Was this with the CDI connected, or not?).

I believe he got that reading on Scorpa (according to the profile info), so values might not be the same for Montesa.

Nevertheless measurements were taken today with the same method as he mentioned (no peak voltage adapter, AC voltage range).
- CDI connected: readings up to 24 VAC.
- CDI disconnected: readings up to 15 VAC

[konrad]

53 minutes ago, Trialeovince said:

-CDI connected: readings up to 24 VAC.

- CDI disconnected: readings up to 15 VAC

Really? I would expect the disconnected (unloaded) reading to be higher than the connected (loaded) reading.

[konrad]

It's possible the system does not operate as I had guessed.  Perhaps the CDI utilizes a DC-DC converter?  That would explain the relatively low voltage observed.  Can you post a picture of your stator?

[Trialeovince]

23 hours ago, konrad said:

I would expect the disconnected (unloaded) reading to be higher than the connected (loaded) reading.

Expectations were the same, but this are actual values.

23 hours ago, konrad said:

Perhaps the CDI utilizes a DC-DC converter?

Unfortunately I have no additional informations about CDI unit.

23 hours ago, konrad said:

Can you post a picture of your stator?

This is the stator of 315R.

Originally posted by "www.trialsbikebreakersuk.com"

[konrad]

I think you will find the exciter coil is the one just right of bottom center.  That coil is physically small for the DC-DC converter approach.  I still feel the voltage you are seeing from that winding is low, but cannot say for certain without reverse-engineering the entire system.  It would at least be possible to rewind that coil by hand.

You could further test the ignition coil by heating it and observing the resistance change in the secondary winding.

You could also use your peak detector on the primary side of the ignition coil (but reverse polarity so the positive lead is grounded.  The CDI capacitor discharges a negative-going pulse into the ignition coil.)  It may be difficult to analyze those results, however.

There's not much more testing you can do without an oscilloscope.

Sorry I can't be more help.

[konrad]

On 7/15/2019 at 2:38 PM, Trialeovince said:

No difference in peak output voltage of exiter coil between spark/no spark event spoted.
Only thing noted was that spark appears when kickstarter is already returned to starting position and not while actual kick. As if spark came with a delay.

I missed this the first time around.  That delay is really weird.  I guess if I had to throw money at the problem, I'd throw it at the CDI before the stator.  

[Trialeovince]

As it was found out, corrosion is not part of the problem and stator couldn't just "die" while the bike was sitting in garage. Same thinking goes for the CDI unit, it couldn't be "fried" as it wasn't getting any energy while bike was standing and it couldn't be corroded as it is sealed with epoxy. Somehow the two were ruled out. Wiring was checked so it was ruled out as well.

One thing that wasn't touched since it was replaced with new part is pick-up coil.
New pick-up coil is not available to buy separately, so a non-OEM part was used (different color code on wires). As it turned out it was not connected as it was supposed to be. Once the two wires were switched, spark appeared with the first kick.

Seems like there is more than just coil in this "pulse generator."
 

Problem solved - polarity of replaced pick-up coil was switched.

 

Most of the time pick-up coil is used in combination with rotor that has some kind of bulge or tooth on it (signal rotor on the attached picture).

But not on this bike. Flywhell/rotor actually has some kind of hole or channel recessed in it.
Could this affect how pick-up coil works? Or is there some other explanation of the problem that was encountered here?

[konrad]

43 minutes ago, Trialeovince said:

 Or is there some other explanation of the problem that was encountered here?

Congratulation on solving the problem! (And thanks for reporting your findings.)

I think the simple explanation is that the pickup coil is polarized.  The leading edge of the trigger structure (whether a tooth or a hole) needed to generate a positive-going (or negative-going) pulse for the CDI to work properly.  The trailing edge would then generate the opposite polarity.  It's not uncommon for both of these events to be needed in order to set the timing and sequence of operations inside the CDI.  Quite frankly, I'm surprised it made any sparks at all.

There has been a lot of innovation in ignition system design over the years -- as much so as engine design, it's just less visible.  It ain't called a "black box" for nothing!

[nigel dabster]

I'm with logic.

Washed and put away. Water ingress is possible. No 1 cause.

Didn't run very well before, swap CDI with a working one. Easy check.

THEN start eleswhere