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Old 03-05-2015, 03:24 PM   #1
imwastefull
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Default Question about Dyna S ignition and coils

I'm putting together a 1974 BT chop. I popped off the points over and the motor came with a Dyna S ignition, dual fire. I've never used one but, assuming it works, i'm going to run it.

My question is with Coils; the Dyna website says to run a 5ohm coil for street use and a 3ohm coil at the strip. I'm building a rigid and will make some longer trips.

Thing is, I have this brand new Emgo 3.9 Ohm coil on the shelf and i'm wondering if i can use it or if there are any draw backs?

Ultimately, I'm able to drop $100 on a brand new coil but i would rather avoid that and run the brand new Emgo that's sitting around.

any thoughts?


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Old 03-05-2015, 03:37 PM   #2
govmule84
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Default Re: Question about Dyna S ignition and coils

I think you'd be fine. 3 ohm coils, I believe, shorten the coil's life at the expense of super-hot spark; you also ask your electrical system to do more work. The DS6-1 (the iggy you have) directions actually call for a coil having 4-5 ohms for street use, so I would think the Emgo should be peachy.

With that said, you could not pay me to run an Emgo coil on a bike that was going far from home.
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Old 03-05-2015, 04:06 PM   #3
Destralo Roach
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Default Re: Question about Dyna S ignition and coils

with the Dyna S the draw back is the mech advance.. you get the same life as with points...

the Dyna 2000i is better with the -83 gold cup...

take a spare points plate and coil with ya

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Old 03-05-2015, 04:47 PM   #4
old.wrench
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Default Re: Question about Dyna S ignition and coils

The Emgo coil should work OK with the Dyna S, although if I was buying a new one I prefer the Dyna coils for my own stuff.
But consider this - I've got a spare 12 volt coil that's been kicking around forever that looks just like your Emgo and it's worked fine on the 3 or 4 different bikes that it's spent time on, including a stint on a bike with a Dyna S ignition.
I put a ton of miles on a Dyna S ignition in a '75 Shovel. The Dyna S is a simple ignition system and in my experience very reliable. I actually liked retaining the stock mechanical advance; I found, to my surprise in fact, that the bike kicked over and fired up just as easy with the Dyna S as with a set of points.

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Old 03-05-2015, 04:59 PM   #5
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Default Re: Question about Dyna S ignition and coils

Yeah, I have video of a fresh built motor I did in a fresh built bike firing on the first compression kick with a Dyna S. That thing was pretty damn reliable, except when it was 28 degrees outside. I liked that ignition, but opted for a mag instead 2-3 years ago.

I know that helps none in terms of your question, but to add two cents to that, I ran 3.5 ohm dual Dyna coils on a single fire setup for about two years with no hiccups. The coils were used when I got them too.
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Old 03-05-2015, 06:05 PM   #6
JAWS
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Default Re: Question about Dyna S ignition and coils

Make damn sure your battery is FULLY charged if you run that and have and electric leg. As the volts drop during cranking the current draw increases and will absolutely cook it. Smoke and all if prolonged start. Meaning extended cranking time.

My advice....until its tuned and you insist on running that ign, keep it on a charger while cranking. Or use points until its a quick starting machine.
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Last edited by JAWS; 03-05-2015 at 06:33 PM.
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Old 03-05-2015, 08:49 PM   #7
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Default Re: Question about Dyna S ignition and coils

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Originally Posted by govmule84 View Post
I think you'd be fine. 3 ohm coils, I believe, shorten the coil's life at the expense of super-hot spark; you also ask your electrical system to do more work.
Mule, you're on the right track but I think the issue is not the life of the coil but the life of the electronic module. Indeed, the more amps the hotter the spark. The coils primary resistance dictates the amperage draw. The module is designed to handle, under ordinary use, the amperage drawn by a 5 ohm coil. As the primary resistance of the coil goes down from there, the amperage the module must handle goes up, up to the point where it can't take the heat and throws in the towel.

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Old 03-05-2015, 09:00 PM   #8
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Default Re: Question about Dyna S ignition and coils

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Make damn sure your battery is FULLY charged if you run that and have and electric leg. As the volts drop during cranking the current draw increases and will absolutely cook
That's strange. Wouldn't Ohms law dictate that as the voltage drops, the current will drop? For example, at 12 volts and 5 ohms of resitance, amps would be 2.4. Since the resistance is constant at 5 ohms, wouldn't the amperage fall off with the voltage? Like 1.2 at 6 volts?

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Old 03-05-2015, 11:10 PM   #9
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Default Re: Question about Dyna S ignition and coils

You know, you are right bob. V=IR...with the lower cranking rpm versus running it must be that the resistance or draw isnt constant in such that the field is steadily building due to the longer durations. Same if the key is on for extended time without running will blow the module and can pop an ignition coil too. When running the field is not as "strong" due to shorter duration.

You are right though the static resistance is the constant, meaning coils and circuitry isnt changed.
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Old 03-06-2015, 07:10 AM   #10
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Default Re: Question about Dyna S ignition and coils

I thought it was a 5 ohm coil for points and 3 ohm for electronic
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Old 03-06-2015, 07:27 AM   #11
imwastefull
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Default Re: Question about Dyna S ignition and coils

Thanks for all the responses guys! Seems pretty unanimous that the 3.9 ohm Emgo coil should work fine. She's kick only and will have a tiny 4 cell sealed battery so I don't have to worry about starter stuff.

The Emgo is brand new so i'll give it a go. If it toasts then I'll drop the dough on a Dyna coil and report back to you all.
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Old 03-06-2015, 07:28 AM   #12
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Default Re: Question about Dyna S ignition and coils

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Originally Posted by the1337aaron View Post
I thought it was a 5 ohm coil for points and 3 ohm for electronic
Yes...You are correct.
And the Dyna-S will last longer [generally] with the higher OHM coil than it will with a Lower ohm coil.
Ohms's law notwithstanding the other law..E=MCsquared will show you what happens.
Neither law was dreamed up before something was Produced...you'll find that all those damn laws were adapted After a thing was working.
Sound Familiar??
Stick with experience...the Higher OHM coil makes the Dyna-S Last longer and Run Cooler....
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Old 03-06-2015, 08:45 AM   #13
bobscogin
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Default Re: Question about Dyna S ignition and coils

This generalization applies: Whether the switching of the coil's primary is done with a set of points or electronically, the greater the amperage the switch has to handle, the shorter the life. If points, it's the pitting effect from arcing, if electronic it's the heat that cooks it. So, how hot do you want that spark?

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Old 03-06-2015, 09:29 AM   #14
Early Iron Motorcycles
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Default Re: Question about Dyna S ignition and coils

imwastefull, I was running duel Emgo's on my knucklehead almost 20 years ago and had no problems at all with the coils or the Dyna ignition, and it was running that way until '04 when I sold the bike, and it was still running them in '06 the last time I saw the bike, and may still be running them now for all I know.
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Old 03-07-2015, 10:16 AM   #15
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Default Re: Question about Dyna S ignition and coils

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Originally Posted by Early Iron Motorcycles View Post
imwastefull, I was running duel Emgo's on my knucklehead almost 20 years ago and had no problems at all with the coils or the Dyna ignition, and it was running that way until '04 when I sold the bike, and it was still running them in '06 the last time I saw the bike, and may still be running them now for all I know.
Probably running them wired in series...with dual fire Iggy...Results in plenty of Primary resistance...Do Not wire in Parallel..I don't believe there would be enough Primary resistance.
I have run many 6V coils wired in series...no Problems
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Old 03-07-2015, 01:28 PM   #16
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Default Re: Question about Dyna S ignition and coils

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I have run many 6V coils wired in series...no Problems
Plus one on that. Used that trick myself; especially on British twins.

Bob
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Old 03-08-2015, 08:40 AM   #17
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Default Re: Question about Dyna S ignition and coils

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Probably running them wired in series...with dual fire Iggy...Results in plenty of Primary resistance...Do Not wire in Parallel..I don't believe there would be enough Primary resistance.
I have run many 6V coils wired in series...no Problems
Single fire with duel plugged heads.
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Old 03-08-2015, 11:21 AM   #18
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Default Re: Question about Dyna S ignition and coils

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Single fire with duel plugged heads.
Single fire with dual plugged heads..You need two dual tower coils..I have used low primary resistance coils on my Dragbike in such an application..but, much prefer a pair of Higher resistance [Points type] coils. Your Dyna S will thank you....
Course..we locked the advance at full also...Not the best for Starting yer street bike!!! Watch that Advance Mechanism Carefully and Religiously.
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Old 03-09-2015, 11:40 AM   #19
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Default Re: Question about Dyna S ignition and coils

I ran dual tower coils like the ones in the picture he posted.
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