CDI test - help verify my results

jasonh

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Jun 23, 2008
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So I've currently got no spark. I did a test on my CDI that should have told me whether or not it was bad. Test showed mine was bad. I was just wondering if someone with a working CDI could run this test just to make sure my test even works at all.

Basically you need a ~6v source. I used 4xAAAs wired in series (because that's what I had handy), but you could use one of those big 6v batteries, a 6v ac/dc adapter, even a 9v battery should work.

So here's what you should do:

connect the black wire to the (-) on the battery.
Ground the spark plug threads to the (-) on the battery.
Tap the blue wire on the (+) of the battery.

Each time you touch the blue wire to the battery, you should get a spark. I did not get a spark.

Someone want to help out and verify these results? If it works, this would be an easy way to test your CDI.

Thanks
 

Tj Bunch

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Jun 18, 2008
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In theory that sounds good but i do not know anything about theese CDI's to know if that will work. And also i would keep at around 6v since that is what theese things put out. My Bike don't sprk so at lunch i may try this to see what i get.
 

jasonh

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Let me know what you find.

I can't afford to just start throwing parts at this thing. My wife is already upset that I got a used one and am having problems. Blah.
 

Tj Bunch

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Is'nt that why we marry them........LoL Mine has not said anything yet but i can tell in her face she don't approve.
 

Bikeguy Joe

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Jan 8, 2008
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I don't know where you heard that, but I just tested a known good CDI and I got nothing....I wouldn't suggest anyone else do it either.

I used a battery charger set at 6v and 10 amps.
 

jasonh

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Odd. I've done it before with a small car version to shock the crap out of people.

Dangit, there goes my great idea.
 

Tj Bunch

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Thanks Joe, I had nothing realy to loose so I did try it nothing Then Pablo was kind enough to Post Ohm Readings and mine is Bad. well now we see how much support i do get from Revolution cycles.....XXXXX Your fingers for me.

Greg
 

jasonh

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I was thinking of try with more along the lines of a 6v wall-adapter that put out just a little current. 10 may be a bit much :(

Either way, my stroke of genius at 9:30pm was completely invalid. Poor me.

Now I have to wait till payday, then order a new cdi and wait for it to be shipped. Assuming I can't figure anything else out.
 

jasonh

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So now this gets me thinking about how these things are actually working.

We don't have a secondary pickup coil signal, so basically these CDI's are only getting a pulse signal every time the crank turns. not only that, but the coil is built in since we don't have an external one. So the thought is, why wouldn't this test work?

I wish I had an old auto coil laying around, because I would like to see what would happen if you just hooked it up to the magneto. I had one in a toolbox, but trashed it when I moved up here :(
 

Tj Bunch

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Jun 18, 2008
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Jason, you need a verry small 6V coil and verry low amp draw the Mags on these egines are verry weak. Thats why they use this type of CDI I think it pushes the power up ro make evrything fire. I have no clue what I'm talking about but it sure sounds good.

Someone said they are a capaciter discharge setup which i Understand but don't know about, also Pablo said there are Diodes in there as well. For what? I thought a megneto was DC current.
 

jasonh

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Magnetos output AC.

Yes, they are called CDI's as in capacitor-discharge-ignition. My beef currently is I cannot find anything about a real CDI that only has 2 wires. Everything I can find basically says this:

A CDI will take a constant power source and keep a charge inside. Then it gets a pulse signal from the motor and releases all that energy into the coil which then steps up the voltage big time and that gets output to the plug which has your lovely little spark.

We only have a power and ground on these, so I don't see how exactly they would work short of just acting like a normal coil and sending out a zap every time the magneto spins around and makes a pulse o' power.

Not to mention, how are these "CDI's" so darn cheap? I can't find cheap Chinese CDI's for under $50-75.
 

Tj Bunch

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Jun 18, 2008
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Thank you I always thought mags were DC i've leared something already.

These buggers are PITA but it will still be fun when we get them running......;)
 

Tj Bunch

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Jun 18, 2008
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Ok I googled and came up with a little more info, About these cdi's PM me for more info.
 
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jasonh

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Yeah, I stumbled on that post as well. Only prob is he says he's never used a China motor. What he's saying about the CDI applies to CDI's in general, except he's saying what I said in my previous post - that a normal CDI will have a power and a ground, and a signal from a secondary pickup coil....our CDI's don't have that. We merely have a power and ground. Hence my confusion :)