Darmah wiring

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BRIAN STUTTS
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Darmah wiring

Post by BRIAN STUTTS » Tue Sep 15, 2015 4:19 pm

Another wiring issue. I am trying to start a Darhma that has been sitting for some years When I press the starter button the motor spins freely (plugs removed and grounded) but there is no spark. As soon as I release the starter button the plugs fire. If I use the kicker it sparks fine. I had this same problem some years ago with another bike but I can't remember what the trouble was but I'm thinking it was a low battery? Any suggestions?

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BevHevSteve
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Re: Darhma wirin

Post by BevHevSteve » Wed Sep 16, 2015 4:52 pm

check your battery voltage then................ `-*
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BRIAN STUTTS
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Re: Darhma wirin

Post by BRIAN STUTTS » Thu Sep 17, 2015 5:27 am

Tried two batteries , both out of running bikes. Both 13+ v and drops to 12+ v when ignition turned on. Hit starter button and they drop to 11+. I put a 3 amp charger on the battery and same thing...no spark on button but popping spark when let up.
Thanx for taking the time to reply.

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Craig in France
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Re: Darhma wirin

Post by Craig in France » Thu Sep 17, 2015 7:59 am

Is the bike still using the original coils and their ballast resistors?

(I have something in mnd ... ;) )

Craig

BRIAN STUTTS
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Re: Darhma wirin

Post by BRIAN STUTTS » Thu Sep 17, 2015 8:29 am

YES.

I talked to a modern Duc mechanic this morning and he said it sounds like the starter button grounds out the coils.

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BevHevSteve
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Re: Darhma wirin

Post by BevHevSteve » Thu Sep 17, 2015 8:40 am

I concur - I was thinking to check the starter relay, switch, motor itself etc.. Just go through the entire circuit and clean, add a bit of dielectric grease to all connectors, clean the brushes while you are at it..................... Check all grounds.
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Craig in France
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Re: Darhma wirin

Post by Craig in France » Thu Sep 17, 2015 11:30 pm

BRIAN STUTTS wrote:I talked to a modern Duc mechanic this morning and he said it sounds like the starter button grounds out the coils.
Hi Brian,

He's on the right line. The plugs are sparking when you release the button because they're discharging to ground. This means that the primary side of the coils are charging ok - which is good news. But for some reason, it would seem that when the starter motor is running and/or the button is pushed in, these primary windings are either not charging or are not collapsing correctly (it's their collapse which generates the high tension pulse in the secondary windings which is what produces the spark).

Just why - ah, that's more difficult to say, especially at long distance. But the fact that the plugs fire on the kicker suggests that the starter system is somehow interfering with the correct operation of the ignition system. One thought I had was that the starter motor (and its associated components) is pulling so much power from the battery that there isn't enuf left to power the coils. This was always recognised as a potential problem, and was the reason why Ducati fitted the type of coils they did (and their ballast resistors) in the first place - the Nippon Denso coils are designed to fire on a reduced voltage.

But if you've still got the original coils and resistors, this sounds less likely.

But do what Steve says. Clean and check all the connections that you can get to in the starter system, not forgetting to check for good grounds. I note you've already got a voltage drop just thru the ignition switch (!) which doesn't bode well for the rest of the now 40+ year old electrical installation. If you haven't overhauled the starter motor recently, 'pound to a penny' the commutator will be full of muck and crud caused by brush wear. Also be aware that the solenoid corrodes badly intenally. It's not worth pulling apart to overhaul. Simply replace it. They were used on a miriad of (mainly) British cars of the period and are cheap on eBay etc.

In the meanwhile, I'll keep thinking ...

BRIAN STUTTS
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Re: Darhma wirin

Post by BRIAN STUTTS » Wed Sep 23, 2015 5:45 am

I went through thru the wiring and cleaned what connections I could reach. The bike cranks easily and runs. It's quite rough but it has been sitting for years and needs attention. At some point the wiring has been "altered" to eliminate the fuse box and wire in in-line fuses up under the steering head. It's a mess up there some it needs some cleaning up. Thanks to everyone that took the time to respond.

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