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Old 05-23-2015, 06:00 PM   #1
blaine.hale OP
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Moto Guzzi Le Mans - no spark

This one is about to drive me nuts, so its thread time! 1978 lemans, all stock minus dyna ignition.
Everything was running and riding fine. I went out to pick up some new plugs and she wouldnt crank back up in the parking lot. I waited a bit, put the new plugs and limped home. After that, I cant get spark at all. I checked for 12v on the ignition unit and it would say around .5v. I thought it was the kill switch on the bars so i flipped it and checked voltage. Killed what little I had, so that was in working order.
Checked coils and even tried new ones with the same result. I reached out to dyna and had my unit tested. They said it was fine and sent it back. Just in case, i bought a new unit and got the same results.
The really weird part is when I plug in one specific red wire from the dyna box to my coils, it is what brings the voltage all the way down. I can actually place that wire on any 12v source on the same bike and it all but kills power to the coils. This wire is the wire that provides power to the dyna unit from the coils.
Also need to mention that check all my grounds and fuses and checked for dity connections. Nothing stood out. Also tried a new mottorad elektric volt reg.
I grounded the dyna on the engine at the valve covers. Theyre very specific about not grounding it on the frame.

Any thoughts?
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Old 05-23-2015, 06:48 PM   #2
bmwrench
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When the Dyna (or points) is charging the coils, it connects them to ground, thus giving a low voltage reading. When triggered to fire by the cam sensor, voltage should rise to just below battery voltage. In other words, spin the motor over and watch for a change from the voltage you saw to battery voltage. If it doesn't rise, there's a problem. Have you looked at the sensor in the "distributer" and the adapter for the trigger magnet?
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Old 05-23-2015, 08:16 PM   #3
blaine.hale OP
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Quote:
Originally Posted by bmwrench View Post
When the Dyna (or points) is charging the coils, it connects them to ground, thus giving a low voltage reading. When triggered to fire by the cam sensor, voltage should rise to just below battery voltage. In other words, spin the motor over and watch for a change from the voltage you saw to battery voltage. If it doesn't rise, there's a problem. Have you looked at the sensor in the "distributer" and the adapter for the trigger magnet?
That makes a lot of sense. I tested it out but my voltage still never peaks above 1volt. Ive only taken the plate off and mounted a new one. I will have to take a closer look at the adapter tomorrow morning. I have a new one from the new setup I can test.
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Old 05-23-2015, 11:37 PM   #4
Andy-Gadget
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When you say you sent the Dyna unit back to them, did you include the triggers?

One possible cause of your described symptoms is a trigger sending back the "close points" or Dwell period signal to the Dyna controller all the time, Dynas don't have a "turn off after a time" feature, which is one of the big problems with them, and they can cook coils if the ignition is left on with the engine in the correct position to do this.

I would look at the signals being sent back to the black box from both the trigger pickups, as the engine is rotated past them.

To change the subject a little, I now use Sachse alternator mounted ignitions on most of my Guzzi's, I have just lent a mate with the Mk1 the correct dizzy mount system to solve his timing problems and as soon as my Mille GT gets home again it is destined to have its motoplat dizzy system, not in use, already triggered from the alternator, changed to the later Sachse system. That way my mechanical hypochondria is appeased, two independent ignition systems. They have little surface mount LED's on the trigger board for each trigger that shows you if they are on or not, and make timing a "no timing light required" job. This feature would show if this is the problem on your Dyna system, as it would be lit all the time.

Mille GT at Salamanka with dead Motoplat ignition.


Back home and "borrowing" the Sachse ingition destined for my Calli 2.
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Andy-Gadget screwed with this post 05-23-2015 at 11:45 PM
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Old 05-23-2015, 11:41 PM   #5
Voltaire
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Probably not relevant but I had a Monza ( probably the same wiring) and I was taking it for test rides after I got it going and it would cut out.
With the meter I could get 12v. It had a Dyna ign unit.
Found the 12 volt power lead to the coils connector was touching enough to give 12v but not enough to power the coils.
Once cleaned and pressed home it worked.
Did my bleedin' head in it did
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Old 05-23-2015, 11:45 PM   #6
England-Kev
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Have you checked your coil with a meter? sorry if I am teaching you how to suck eggs, but we shall make sure.

disconnect the coil..

set your meter to Ohms (little horseshoe sign) and choose the lowest setting..

put the probes on the two small coil connections, one each side, you should get a reading close to the coil spec (1.8?)

if that is good, then change the meter to a higher setting (200k)

now go from one of the small terminals, to the plug cap. you should also get a reading here, if not then the coil is shot.
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Old 05-24-2015, 07:45 AM   #7
blaine.hale OP
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I did check the ohms, all was well :)
All connections are clean, too! You guys got me thinking it's the magnet for the dyna unit that spins off the cam. I actually did not send that back to dyna for testing (3 weeks ago) because I thought it was just a solid piece with nothing to go wrong.
I'll put the new one on today and see what happens.
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Old 05-24-2015, 08:40 AM   #8
Tim McKittrick
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When I purchased my lemans III it had no spark. It also has a Dyna ignition with a Dyna coils, and the bike had been into the dealer several times before I got it for mysterious misfire issues which had never been solved.

In my case the problem turned out to be the grounding wire from the Dyna control box. It was attatched to the negative terminal of the battery and not to the engine itself, as directed in the Dyna installation guide. Once moved the Goose once again had a strong healthy spark.

It appears that the misplaced ground was responsible for both the misfire problem and finally the full loss of spark. I would have thought the ground location to be unimportant, but the guide is quite adamant that it must be to the motor itself.
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Old 05-24-2015, 01:10 PM   #9
blaine.hale OP
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Quote:
Originally Posted by Tim McKittrick View Post
When I purchased my lemans III it had no spark. It also has a Dyna ignition with a Dyna coils, and the bike had been into the dealer several times before I got it for mysterious misfire issues which had never been solved.

In my case the problem turned out to be the grounding wire from the Dyna control box. It was attatched to the negative terminal of the battery and not to the engine itself, as directed in the Dyna installation guide. Once moved the Goose once again had a strong healthy spark.

It appears that the misplaced ground was responsible for both the misfire problem and finally the full loss of spark. I would have thought the ground location to be unimportant, but the guide is quite adamant that it must be to the motor itself.
When I got mine, the ground for the dyna unit was on the battery negative terminal as well. It actually ran just fine the whole time like that but I was told to quickly remove it from there and ground it to the motor (not the frame.)
I'm down in the basement fiddling with the magnet...of course I'm one for scope creep and saw that the whole ignition unit off the cam was dirty so I pulled everything out and scrubbed it down and re-installed. I'm at the point of remounting the magnet and following the provided instructions on which direction to put it.
Is it possible that the previous one was so far out of placement that it just wouldn't spark? I never recall getting it timed just right. It was always a bit weird.
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Old 05-24-2015, 02:07 PM   #10
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Well, no dice on replacing the little magnet on the cam and aligning it correctly.

Looks like I'm back to unplugging things and hunting down bad grounds. For the record, My coils got readings of 3.6-3.8 ohm. The dyna support I got said that was sufficient for generating spark.
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Old 05-24-2015, 07:03 PM   #11
bmwrench
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I've sent a couple of Dynas back for testing. They always said there was nothing wrong with their stuff, but I had to replace them. I'm not a fan.
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Old 05-24-2015, 07:49 PM   #12
LAkevin
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I have a LM2 and...

you should really check the grounds at the side mounted electronics. The deal is, all those bolted up parts will give you fits of high resistance connections. With a meter set on ohms, you won't notice the high resistance. Under load, however, voltage drop increases with the square of the value of the current. It's called I squared R loss. I troubleshot mine by using a automotive jumper cable connected from neg terminal on battery to an engine bolt, and the other clip from that same bolt to the ignition module.

What I've done on my bike to solve this is add additional ground wires to tie everything together. I've also fixed a friend's with the same technique.

Think about all the bolt up connections between the ground and the ignition box. Each one is a potential ground loop.
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Old 05-25-2015, 01:54 AM   #13
Andy-Gadget
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Quote:
Originally Posted by blaine.hale View Post
Well, no dice on replacing the little magnet on the cam and aligning it correctly.

Looks like I'm back to unplugging things and hunting down bad grounds. For the record, My coils got readings of 3.6-3.8 ohm. The dyna support I got said that was sufficient for generating spark.
If it is the pick ups that are at fault, changing the magnet won't make any difference, as if I suspect is the case that the trigger for one coil is on all the time.

I don't have the Dyna wiring available, at sea with very slow satellite internet, but you should be able to detect a change in the outputs of the triggers as the magnet passes them, or test them with the magnet removed and see if the output is the same between the two triggers.

I am not a fan of Dyna as well, even though my Calli 2 didn't disgrace itself with its Dyna 3, I just don't trust them.
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Old 05-25-2015, 06:45 AM   #14
blaine.hale OP
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I would say I'm not a fan of Dyna but it seems off that 2 units, 1 being out of the box new, would be the culprit here. If only I had the mechanical points unit to test all of this out!
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Old 05-25-2015, 07:42 AM   #15
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I have a points set I took off my T3 if you're interested.

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