Checking Coil Output on DMC2/Witt Equipped 3C

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laverlesmains

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So far I've installed the following on my 1975 3C

1) the DMC2 (running Curve 1 for now)
2) a SH R/R
3) new coils
4) relay wired up for direct voltage to the ignition coils.
5) New NGK plug caps - these are the type that "screw" into the end of the coil wires. 

There are a few issues yet to resolve, one of which may be weak spark on 1 & 3.    I noticed it when trying to set the timing w/ the strobe.    I was getting a nice strong even light when the inductive clamp was on #2 spark plug lead, but when connected to #3 the light seemed to be weaker and somewhat intermittent - may <2% of the time it wouldn't flash.   Weak spark and intermittent may be two different problems, the latter possibly related to pickup gap..

How do I go about determining the strength of the spark or output from the coils?  

Measurements so far:

1) Resistance of the pickups 57-59ohms
2) Battery voltage (not running) 12.7V
3) Voltage at coils (not running) 12.7V
4) resistance across Coil for #2 = 4.5ohms,  resistance across coil for #1 & #3 = 3.5 ohms.    Why the difference?


Thanks, Tim

 
definitely an issue w/ #1 and #3 spark strength...    plugs 1-3 from left to right

I've got a nice new set of Dynas on my 1979 GS750E.    Any issues in taking one of them and replacing the dual coil on the Laverda? 

IMG_0469.JPG
 
Hi Tim

I think the problem is more a problem of setting the adjusting screw of idle

I had the same colors recently. Setting, and good colors to the three spark plugs

Cordialement

Xavier
 
Xavier

Yes..  I know I still have idle settings to modify..  but didn't want to confuse two or more possible problems with each other.

I did replace the coil with a 5 ohm Dyna from my Suzuki and wired it up.      The bike started much stronger and settled into an idle much better and the strobe light is much stronger.

I still have adjusting to do to the mixture, as well as set the timing, but for now I think I'll reach out to the supplier and check about replacement coils.

Cheers, Tim
 
Christ there's too many Tim's on this forum , From now on I shall call myself Max Power to avoid confusion . I used Tec coils from a Vfr and cb Honda . I'm sure I've a spare dual output kicking around if you want to try it ?
                              Max P
 
all hail Max Power.

thanks for the offer..  but as noted I did take a new Dyna dualie from the Suzuki, installed it, and it seemed to make a difference.    However, after a plod down the road and back it was still idling off and breaking down around 2/3 throttle.  I have been putting off checking the floats & balance on the carbs so returned to the garage to take it all apart and return the coil to the Suzuki.  No use having two bikes out of service.

I reinstalled the coil from Wolfgang's DMC kit, and set about removing the carbs.    I removed float bowls and found that 2 of the three floats were about 21-22mm instead of 18.5ish..  This could account for the bike breaking up under higher throttle??  Floats not letting enough gas into the bowl?    So I adjusted them all to be about 18.5mm.      I did the drill bit balancing on the throttle slides and found that #1 and #3 were more closed (I think that's the technical description) than #2 so I adjusted them with the worm screws on the linkage.

With floats and slides adjusted I buttoned it all up (with the suspect coil installed), set the idle, and took it down the road.    Much crisper response to the throttle, settled down to an idle at the stoplight, and although it was breaking down a bit at 60-70% throttle it would pick up nicely again if I gave it a little more gas and let it rev higher.    I've got the tach and speedo off and in pieces on my bench so I can't tell what RPM it was breaking up at, but since it exhibited this behaviour with the old  BTZ and the new DMC systems, it has to be fuel related so maybe I'll set the floats to 17.5ish. 

Anyway..  the coil thing (3.5ohm vs. 4.5ohm) may be a red herring, but I'll wait to see what Wolfgang says in response to my email.

Cheers

Tim
 
That's bound to cause confusion, mind if I just call you Tim?

 
I'm not any kind of expert on ignition systems, but I reckon the coil resistance may have something to do with your problem. Electronic ignitions generally like to run coils of around 3 Ohm primary resistance. 4.5 Ohm will reduce the spark energy quite a bit, especially on a dual coil where the spark has to jump twice the gap (two gaps in series).

Find a better duoble coil.

Cheers,
Cam
 
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