Stumble / Cut Out / Hesitation at Specific RPM

  • Thread starter Thread starter laverlesmains
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It could be the feed wire from ignition to coils
Click to expand...

Right now the coils are fed via a relay....  so if the wire from the ignition to the relay is flakey, then yes it could cause the problem...   

Will keep checking...    I'm wondering if it isn't something in the stator whereby the output signal gets erratic at a specific RPM due to some interference from the alternator or some other magical electrickery
 
Well there you are, it looks like you're going to have to scrap it, let me know how much you want for the old thing !.  :D :D :D
 
a bit of a frustrating day.... 

Started of trying to rig up a little idiot light display using some 12V LEDs..  Connect one to the +ve lead to the coils, and a second to the trigger lead to the coil..    My hunch is that the trigger coils on the stator get confused at a certain RPM and send enough errant voltage to the DMC that it shuts down.  If so - I'd see one of the idiot lights go out while the bike was stumbling.  However, the LEDs seemed to introduce resistance or some other electrical magickery, and the bike wasn't running well, so I ripped it all out and thought I'd just take it out on the road to see if the stumble was better since I'd bypassed the connector block.

Throwing caution to the wind I of course headed for the multilane highway, and of course after about 10 minutes she started to hiccup and stranded me at the side of the road.  Luckily the offramp was about 1/2 mile away and I managed to get my monthly cardio and weight training in ....  Thinking the DMC might need a power off / reset I disconnected it, waited a minute, then connected it back up.  Sure enough it started - roughly - and made it about 50 feet before dying again.

Called the missus, called the towing company, got the bike home, and after a nice 1 hr rest she started up again.

So..  I'm thinking it's electrical and not fuel related.  I'm also thinking that the DMC is getting mucked up somehow..  So my question is "what mucks up a DMC?"  Voltage spikes? Erratic voltage from the stator triggers?  Distance from home?  Number of miles from the nearest offramp?



 
Tim - sorry to hear you're still struggling to find the problem.  Back to an earlier post - you said you had similar symptoms with the old ignition system as well as now with the DMC.  The only common item is the trigger coils.   You also said that you measured a difference in resistance between the two trigger coils.  After 37 years, they are past their best with failing insulation a likely culprit.  The wiring can be replaced with care. Worth doing using heat resistant wiring and check again.  The trigger coils themselves can occasionally fail or become susceptible to the effects of heat.  Replacement is the only answer.  There are reports of Japanese TEK triggers being used with suitable mounting brackets instead of the original Bosch items...John Wilson (IIS) has experience of this.

http://www.laverdaforum.com/forum/index.php?topic=41065.0
http://www.laverdaforum.com/forum/index.php?topic=45851.0
 
Rob

Thanks for the feedback & the links.  I'll check to see if I can get a replacement stator first, then maybe look into the Tek alternatives.

Cheers, Tim
 
Agreed - here's a picture of my trigger in its original state and one after I'd cleaned up the wiring.

There is a tiny bit of wiring exposed as it enters the trigger - some folks put a form of epoxy over that part to seal it..  Any thoughts on which epoxy?

IMG_0439.jpg


IMG_0440.jpg



 
Looking at the verdigris on the trigger wiring, I wonder about the condition of the stranded wire conductor itself.  How did you clean it up? The trigger output is tiny (nowhere near enough to fire a 12v LED!), and needs all the help it can get to find its way to the ignition box.  The remaining debris where the conductor passes into the epoxy of the trigger unit is a concern too....is there anything bridging the two connections?

I agree the best bet is to try and find another stator plate in better condition.  As far as epoxying those connections, I'd prefer to use an acetone-free RTV silicone like ACC Silicones AS1701 (not conventional RTV silicone which attacks copper conductor!)  That will provide flexible support for the conductor and avoid the risk of it fracturing.

 
 
I cleaned off the corrosion w/ emory cloth & contact cleaner.    I'm getting 57-59 ohms resistance from the trigger, so I'm fairly sure that it's not bridging.

However, I think I'll look for the silicone, ensure it's not bridging, and then seal it up.
 
OK - still leaves the possibility of a trigger failing as it gets hot.  Have you checked insulation resistance to earth (stator plate)? Think there have been reports of heat related failures - could always try blasting a hair dryer at 'em to see what happens.  Doesn't fully replicate the vibration of a real operating environment, but at least another step along the way!
 
just to rule it out, I directly connected the ignition coils to the battery and bypassed the kill switch..

Took it down the road and it broke up at the same RPM...  So it looks to be RPM/vibration related as opposed to heat related.  Maybe I'll tape a multimeter to the dashboard and see what happens to the trigger voltage when the RPMs break up.

 
Maybe I'll tape a multimeter to the dashboard and see what happens to the trigger voltage when the RPMs break up.
Click to expand...

I think you'll need an oscilloscope to see what's happening with any degree of certainty...a multimeter may not react fast enough to cope with the pulses being generated at anything over cranking speed.  Don't know if you read this thread...others have suffered similar symptoms  :(

http://www.laverdaforum.com/forum/index.php?topic=41065.0
 
if I can find one that'll fit then taping the oscilloscope will be next :o

When riding, the trigger puts out about 3-5Volts, rising to about 6V when it starts breaking up and if I push through it to redline it's about 7 V.

Interestingly, the other trigger (for #2 cylinder seems to put out only 1/2 of that.

I didn't think that triggers put out  that much voltage - unless my range is wrong and it's really 0.3 - 0.5 rising to 0.6 and then to 0.7 VAC

IMG_0493.JPG
 
At the risk of stating the blindingly obvious, both outputs should be the same!  :)  Just need to work out which one is wrong....could be all sorts happening that messes up the pulse and I have no idea what he HKZ black box is looking for in terms of input.  Wonder if some kind soul could help out with a spare stator plate for you to try?
 
As the output is a waveform with frequency increasing with revs (eg. waveform on following link) the multimeter might be a bit of a blunt instrument. http://www.diycardoctor.com/current_ramping.htm - if you can get hold of a storage scope you can go back over the results once you have run the test..

Just a though given that you're in the bay area (which probably has one of the biggest concentration of oscilloscopes in the known universe) - SF State has this experiment on their Electrical Engineering Syllabus - it might be worth a call to see if anyone would like to learn how to use an scope with a real world example!
http://online.sfsu.edu/~larryk/engr206/Experiment%206.pdf

Otherwise a local techie forum might be worth a try to see if anyone can help
 
Thinking about it, a simple test would be to hook up strobe light (pref. with inductive pick-up) and see how consistently it flashes as you hold the trigger and rev the engine (for each plug in turn) - it would be obvious if a spark is missed.

NB if it does miss it can also be a problem downstream (are plugs fouled) as well as upstream (coil, etc)...
 
BrianC

Interesting that you should mention the timing light..  One of the things I've noticed during this whole process was that my timing light seemed to have difficulty in picking up a signal on #3 sometimes, and occasionally on #2..  With all the idling in the garage, the plugs have gotten sooty and that may cause the problem...   

Much to be sorted out.  Just have to make sure I'm only changing/fixing one thing at a time else the problem will be "solved" without a frickin clue to what I actually fixed.

And yes, an oscilloscope is on my wishlist.  SF craigslist provided this heap of magic that would look great in the garage:

heap%2520of%2520stuff.jpg
 
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