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Trialeovince

Montesa Cota 315R - no spark issue

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So here goes the story. Bike was lightly rinsed with water after riding (with garden hose - to remove chunkier pieces of mud) and later started so it dried out. Then It was stored for a year or so.
When I attempted to start it there was no life in it - no spark. All coils were checked via resistance test and were OK (according to values in users manual) apart from pick-up coil which was bad (infinite resistance). Seems like some water came in stator department via hole for breather tube and damaged pick-up coil. But then again bike was never easy to start anyway..

New pick-up coil was fitted but the problem persists, only now it throws spark from time to time randomly. Sometimes strong, sometimes weak, most of the time none at all. If bike is left to stand for couple of minutes spark appears after 3rd or 4th kick. After that none, not until bike is left to stand a couple of minutes again. Then the process repeats: spark or two after 3rd kick and then none.

What has been done so far:
- all stator coils tested for resistance - OK
- pick-up coil tested for resistance - OK
- ignition coil tested for resistance - OK
- spark plug lead (with and without cap) tested for resistance - OK
- new spark plug (NGK BR6ES) fitted and adjusted according to users manual
- both "grounds" cleaned and checked for continuity - OK
- all cables/leads from stator dpt. to CDI unit checked for continuity - OK
- all cables/leads from CDI unit to connectors checked for continuity - OK
- "stop" button measured (OK), then disconnected just to be sure
- voltage from voltage regulator around 12,4V while kickstarting

Peak voltages were also measured (via peak-voltage adapter, all connectors disconnected while measuring):
- pick-up coil gives from 8 to 13V while kickstarting
- charging coil (usually connected to voltage regulator) gives around 20V while kickstarting
- exciter coil (usually connected to CDI) gives same 20V while kickstarting

Does anyone know if these peak voltages are OK (not specified in users manual)?
Or if someone could measure them on working Cota 315R that would be great.

If all this is normal, then only one thing remains - CDI unit. Any ideas how to test it? New one is hard to get and not at all cheap, so I would like to be sure it is bad before ordering one.
If somone could check continuity between "ground" and green-white wire on CDI side (while disconnected from pick-up coil) I would also be gratefull. Mine reads "0" - it is shorted to ground.

Any other ideas what to check?

Edited by Trialeovince

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33 minutes ago, Trialeovince said:

 charging coil gives around 20V while kickstarting

 exciter coil gives same 20V while kickstarting

I have no experience with this particular model, and I'm not sure about your nomenclature. 

But... for the winding that goes to the CDI (not to the voltage regulator) I would expect to see closer to 100V while kicking.   How are you measuring the "peak" voltage?

The output of that winding is dependent on RPM.  I would suggest  "motoring" the engine with an electric drill via the flywheel nut (you may have to get creative with a socket/adapter etc.)   I generally do this with the head off, but just removing the spark plug may give you a clue.

P.S. you've done a good job troubleshooting so far!

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Didi you actually remove the stator. All the mounting bolts could have corrodid. Always good to remove and clean/lube any bolt that is a grounding source. Also trim back the spark plug lead to fresh wire 

 

 

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38 minutes ago, konrad said:

... and I'm not sure about your nomenclature.

- charging coil (connected to voltage regulator) gives around 20V while kickstarting
- exciter coil (connected to CDI) gives same 20V while kickstarting
 

39 minutes ago, konrad said:

IHow are you measuring the "peak" voltage?

With peak-voltage adapter and multimeter, spark plug removed from engine while measuring
 

40 minutes ago, konrad said:

I would suggest  "motoring" the engine with an electric drill via the flywheel nut (you may have to get creative with a socket/adapter etc.).

Stator and pick-up coils are mounted on flywhell cover. If cover is removed, no electricity will be produced.

 

14 minutes ago, lineaway said:

Didi you actually remove the stator?

As mentioned flywheel cover with mounted stator coils were removed from engine. But I did not separate stator from flywheel cover. Do you think stator is grounded via cover?

 

19 minutes ago, lineaway said:

Also trim back the spark plug lead to fresh wire.

Even when resistance readings are OK?

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

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Also, try measuring the peak exciter voltage with the CDI disconnected.  The CDI may be loading that coil too heavily.

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15 minutes ago, konrad said:

Also, try measuring the peak exciter voltage with the CDI disconnected.  The CDI may be loading that coil too heavily.

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).

 

16 minutes ago, konrad said:

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

As mentioned everything was disconnected while taking measurements so I am unable to give you the answer at the moment, however I will try this out.

 

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 You more likely have a corrosion problem, from sitting than anything else. 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. 

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Probably would not hurt to post a scan/photo/screenshot of your wiring diagram, as I am not familiar with that system.

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1 hour ago, lineaway said:

 You more likely have a corrosion problem, from sitting than anything else. 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. 

Will defenitly check.

 

14 minutes ago, konrad said:

Probably would not hurt to post a scan/photo/screenshot of your wiring diagram, as I am not familiar with that system.

Here it is:

SAVE0021.JPG

Original post::
https://www.trialscentral.com/forums/topic/4980-cota-315r-help-needed/

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The two power coils in the alternator are "floating" so there's nothing to ground (therefore corrosion of the alternator cover bolts can't cause your problem).

The G/W wire from the ignition pulse generator connecting internal to the CDI ground wire is not necessarily a problem (and would be unlikely to cause the intermittent symptoms you describe).

 

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I typically see 20 to 30 VAC from the exciter coil kicking it over without a peak voltage adapter. It sounds like that might be a bit low. What is the ohms range given in the manual and what does your exciter coil read?

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

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9 hours ago, cascadeimp1 said:

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

Excellent question!  And, at what temperature is it being measured?

Although resistance readings can help find a defective coil, they can't guarantee proper operation.

I expect your exciter coil will be comprised of many turns of fairly fine wire.   Even a few shorted turns will cause it not to work properly, yet the resistance reading will be essentially unchanged.

The fact that your pickup coil was inoperable also may be a clue to damage by water.

Another test is to measure the resistance of the suspect coil while heating it with something like a hair dryer.   Copper wire has a positive temperature coefficient of ~0.4% per degree C.  You should see the coil's resistance increase gradually as you heat it.  If, however, the resistance drops suddenly, this indicates a problem.

 

Edited by konrad

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One of the drawbacks of trying to quantify the AC voltage produced by a motorcycle stator coil is that the waveform is nothing like a sinusoid, and different meters will measure it differently.

That makes a compelling reason to buy or build a peak detector.  See: https://thumpertalk.com/forums/topic/1034259-build-your-own-peak-voltage-adapter/A

Although be aware that different values of the resistor and capacitor (and the input impedance of the meter itself) can give rise to different readings as well.

That's all I can contribute for a while, as I'm off to do a trials now.

 

Edited by konrad

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