Problems getting a spark, CDI fried? Help!

Kadupult

New Member
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3:21 PM
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Dec 31, 2013
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Location
Texas
Hello all! I have had some real problems with my electrical components building this 2 stroke, the first stock CDI that came with the kit I received was completely dead on the ohmmeter, wouldn't spark at all. ordered a new one and after replacing the CDI and the magneto, it started for the first time yesterday. But only a mile down the road I stopped getting spark and once again, tested with an ohmmeter, dead CDI:cry:. tested the magneto, its seems fine. What is causing this? Am I frying my CDI? How can I fix this? Thanks!

EDIT: I would like to also point out that this is a brand new engine, CDI and magneto... So it seems odd to me that just riding the bike less than 3 miles would kill the CDI. I've read on here how unlikely that is, so I feel as though I'm doing something wrong, maybe not grounding correctly?

Thanks for all the help. I really appreciate all the information on these forums.
 
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would be nice if a CDI tester or a second bike were handy to test it - it may just be a wire that is bad inside its insulation or a connector hanging by one strand or something like that that is a problem with the bike instead of the CDI

anyone local to you that you can try it with?
 
anyone local to you that you can try it with?

Sadly no, I'm alone in this one. I don't think the bike did anything to the wires this early on, I've gone less than 5 miles on this bike since this kit has been out of the box. but it's a possibility, I won't rule it out. How could I find that out for sure? As I stated before, the CDI isn't showing up with any reading at all on an ohmmeter, so I'm pretty sure that's the problem. I would also like to know how to avoid this problem in the future in addition to knowing how to fix this. (hopefully I can do SOMETHING besides ordering a third CDI)

Thanks for the help!
 
unless you get someone from Texas to PM you, you may be stuck

some weirdness with a bad solder connection in those new wires may be causing it, or I once opened two CDI boxes in a row with bad CDIs in them - no way to test these without building a CDI tester, since many go bad with a fat spark, but wrong timing
 
A fat spark and wrong timing can kill the CDI? interesting, that may have been my problem, I was trying out a high performance three ponged spark plug from BB when this happened. I'll try to strip off some insulation to get a reading today, will post results.
 
no, fat spark doesn't hurt timing, it's just that you need both good spark AND correct timing to run

I've seen CDIs that had a good spark but wouldn't run the motor - that's why I built my tester with a spark plug so I can see the spark and timing marks so I can see when it fires

I have also seen a painted motor where the washers under the head bolts were painted giving no ground to the head - spark plug only sparked when you held it on a muffler nut

if you can hold the plug in your hand and get no 'bite' when you roll the bike and can see a short 'blip' on your meter hooked from blue wire to ground when you roll the bike, then CDI is probably bad
 
Oh I see. well the last thing I heard before the engine died was a sharp snapping sound, but that could have easily been anything, even gravel just hitting the frame. But I convinced myself it was the sound of something breaking.

I might have to build a tester, I know it was doing alright at first, it was running really well for about 30 minutes and then it suddenly just stopped getting spark. The reason I think it isn't timing, is that I've done spark plug tests and haven't seen a single spark since the moment it died.

I don't have any paint on the motor, and I know when it was working it would spark just fine against the engine.

As for stripping the insulation around the wires, did that and not even a flicker on the ohmmeter. It's definitely a dead CDI... but how?!

I'm going to order another CDI or two in the meantime, I'm starting to really not trust these things... Anyone know of a vendor that sells reliable CDIs? Maybe even a higher quality alternative?

Any idea of what I could be doing to cause both of my CDIs to die so quickly? Maybe I'm just really unlucky. I would hate to buy a third one, just to have it fry because I've been making a mistake this whole time.
 
ohmmeter? sounds archaic. i hope its actually a multi meter with various functions...such as continuity/diode check!

you will only get high resistance or open readings across cdi wires, blue and black.

with diode check, youll have a diode reading one direction, nothing the other way.

should have a fairly low resistance between the plug lead and the black wire. not silly low, not silly high... a couple of K from memory.

also check for continuity between plug leads and all bits earthed, such as the head mentioned previously...

most posters here are agreed that the cdi unit itself rarely dies. the magneto section, all the time.

snapping sound...are you sure the magnet on the crankshaft is even spinning? someone had a snapped crank here at one point...

check everything. cant be that hard, theres only two wires!


dont bother with the multi prong plugs ;) spark still only jumps the one gap. iridium/plat plugs on the other hand...personal choice.
 
Here's a tip that I got from Jaguar:

Disconnect the CDI from the stator coil. Connect an AC voltmeter to the coil wires (blue and black). Push the bike with the spark plug removed and see how much voltage is generated. I have seen as much as 50 volts on mine. Drastically less indicates a bad coil. If the voltage is suficient then all that is left is the CDI/high-voltage-coil, assuming that the spark plug isnt screwed up.

Chris
AKA: BigBlue
 
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