whats the difference between an AC Ignition coil and a DC one?

Im puttering around with the 1974 Honda XL 350...and the coil puts out a weak spark...It may have something to do with the fact the lead wire to
the plug is only held on with the internal wire..the insulation is broken around where its molded into the coil itself. I suppose I could repair that with JB weld. The condenser is also molded as part of the coil, and it may be bad, so I picked up a used condenser from a bike yard and will splice it in.
I picked up a used generic 6vt coil for $10, and machined a mount to adapt it to the bike. I tested the coil by grounding the hot lead by scratching it to the frame and after 10 or 15 sparks, the coil split around the circumference . It doesnt spark anymore...shrug. It had no condenser attached to it. It "bumped" pretty good each time I sparked it. Had a nice brite spark too.
Im testing the electrical with a 6vt battery charger hooked into place of the battery
The wiring diagram I have and all references say that the Honda uses an AC coil, fed by an ignition winding on the alternator. Honda wants $80 for a replacement coil, JC Whitney sells an aftermarket "can" coil for $21, but doesnt indicate if its AC or DC.
Whats the difference between an AC and a DC coil????
Anyone got a surplus manual for a 1974-75 Honda XL 350?
Gunner
"They couldn't hit an elephant at this dist..." Maj. Gen. John Sedgewick, killed by a sniper in 1864 at the battle of Spotsylvania
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Gunner Asch wrote:

Gunner , think about it for a minute - if that voltage input to the coil was AC , it'd be buzzin' all the time . There's gotta be a diode , or more likely a plate rectifier (My '74 CB750 has one of those on the 3 phase output from the alt coils) between that coil and the supply .
And a metal-filled epoxy on a high-voltage application ? The weak spark is more likely from a bad cap . Do ya get like a giant spark when ya break the circuit ? Sure sign of a bad cap .
--
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On Sun, 23 Nov 2008 15:23:07 -0600, "Terry Coombs"

Here is the wiring diagram...check it out for yourself
http://www.cmsnl.com/classic-honda-fansite/honda_wiring_diagrams/XL350.jpg
Thanks guys for the heads up on JB Weld..Id not remembered that it was metal filled.
Gunner
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Gunner Asch wrote:

If I'd had my head in the light , I'd have realized that the ignition system is basically a magneto with the coils in separate units . Hey , embarassment can lead to learning too !
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I've got a bit of info on the XL250 from an old Chilton, but nothing on the 350. Indeed, the wiring diagram shows a separate winding on the alternator for the ignition and an "AC ignition coil"-no rectifiers. You should be able to rewire so to use a regular 6V coil. I can try to scan the wiring diagram and send that to you if it's any help, but there's nothing in the Chilton about that alternator.
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Rick wrote:

I'd sure like to see details of that system ! How do they time the spark ? Kinda makes sense , AC will give a continuous spark , or rather arc ? Learn something new every day !
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It appears to be essentially a magneto winding..still uses points and a condenser.
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Not sure of the difference but there surely is one. The old Ducati singles used both. Street bikes with batteries had the DC coil, the scramblers with magnetos had an AC coil. If you need an AC coil, try some motorcycle boneyards and look for dirt bikes, which generally all run mags. Also, I'll bet you could find a used coil on ebay for far less than the dealer wants.
Speaking of which, I remember Dirt Bike magazine running an article in I think the late 70's, touting how anyone could have their own $10,000 MX bike. Back then, those dollars meant works bikes. Well, all one had to do to own such an expensive bike was buy it one single part at a time. The markup is huge!
Jon
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The markup on parts is usually more than the markup on the whole ;(
Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
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Gunner Asch laid this down on his screen :

If the battery is used for the ignition, which I don't know that is or not, then you'll probably need a battery, not a battery charger.
You can see a listing of parts here http://www.bikebandit.com/houseofmotorcycles/honda-motorcycle-xl350-1974/o/m9383
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Gunner Asch wrote:

Check your Email
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Steve W.

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On Sun, 23 Nov 2008 13:06:24 -0800, Gunner Asch

Do NOT use JB weld, it is metal filled and slightly conductive. Best is plasic bumper repair epoxy, or winsheild mounting urethane. Plain epoxy works pretty well too, but the bumper stuff stays flexible.

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On Nov 23, 4:02pm, snipped-for-privacy@snyder.on.ca wrote:

Being the curious type, and having seen before the statement about JB weld being slightly conductive, I decided to see if it was true.
I have a number of pallets made of scrap circuit board material and JB Weld epoxy. The pallets carry circuit boards or panels of boards through our convection oven to solder the surface mount components to the boards. We use both leaded and lead free solder paste, so it gets very hot. JB Weld is the only common epoxy that will stand the heat over and over.
I checked the JB Weld on a pallet with a hand held DVM set to read 20 meg ohms. No matter how close I set the test leads, they showed a complete open circuit. If JB Weld is slightly conductive, it must be extremely slight!!! It should work just fine to repair electrical parts, including ignition coils.
Paul
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snipped-for-privacy@coinet.com wrote:

Now try it while running 20-30 kv though it. It's amazing how items that show no conductivity at 9 volts conduct just fine at high voltage.
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Steve W.
Near Cooperstown, New York
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That's true, Steve. But is the base material conducting or is it the surface contamination?
Paul
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snipped-for-privacy@coinet.com wrote:

When the voltage burns through it in multiple places I would say the problem is the base material. It doesn't insulate high voltage very well. I have tried JB weld for this same application. It burned through and arced from the moment the current hit the repair.
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Steve W.
Near Cooperstown, New York
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I suppose some would accuse us of hijacking Gunner's post, but some may learn from our discussion.
Probably any regular epoxy would fail when the voltage is sufficient. We have a customer that must test his circuit boards at 6kv. His new design arc'd between leads of through-hole resistors. A quick fix using corona dope was tried. Didn't work. More layers of corona dope. Still arced. Had to do a board redesign to reorient the resistors to give about 3/4 inch spacing between leads. That to cured the problem.
I don't know what is in corona dope, but in the 1950's we used to repair TV flyback transformers with it. Why it didn't work on the resistors is unknown.
Paul
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One of my former jobs was testing the insulation on some motor housings, we tested at 20kv normally. I got to "play" with other insulating materials as well.
Most corona dope is nothing but a thick enamel or solvent dissolved polystyrene material. About 4kv per mil was the rating on the stuff I used. The problem in your case may have simply been that the hole spacing was tight enough that no insulation would have worked unless you could make the arc path itself longer.
One of the other folks in our plant used to say that the testing I was doing was scary. Then I mentioned that the powder gun he used daily ran at a 40kv charge. His eyes turned into saucers then.
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Steve W.
Near Cooperstown, New York
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In article
[snip]

It's a polyurethane varnish. Google on "corona dope", go to the GC/Waldon website, and look at the MSDS.
Joe Gwinn
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Maybe waaaaaaay off course - could the AC refer to AC Delco rather than A.C. // D.C.
The AC / DC doesn't make much sense. AFAIK the primary difference with older (car) coils was if they had in internal or external ballast resistor.
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