Troubleshooting CDI ignition.

turbofiat124 · 10-25-2019, 06:07 AM

I'm trying to troubleshoot why a co-worker's Kymco 90 Mongoose has no spark. This is my first troubleshooting experience with a CDI ignition system.

I've troubleshooted this bike for a couple of hours using the wiring diagram.

There are two wires going to the coil. The black/yellow wire comes from the CDI and is connected to the black pin on the coil. When the engine is cranked over, using a test light, the test light pulsates when connected to the black/yellow wire.

The green wire which goes to the green pin on the coil goes to the kill switch which finds it's way to ground when the switch is closed. At least that is the what the wiring diagram shows it. I disconnected it just to rule this out.

This is how the kill wire works correct? Just like a lawnmower engine there is a ground wire coming off the coil. When grounded, it kills spark to the engine.

On this ATV, this wire does the same thing, correct? Meaning if disconnected, the coil should still function. The coil itself is grounded through the mounting screw so this wire should have no other function. It is not necessary for the wire to be connected to the coil for it to actually function, correct? Does this make sense?

When the spark plug is installed on another engine and checked for spark it fires. But when hooked to this coil does nothing.

My co-worker said the bike just stopped running one day so he tried installing a new spark plug. He did not properly gap it but I did tonight.

He had someone else work on it before me. I have no idea what this guy did but he tried installing a new CDI and a new coil but still couldn't get it to fire. He gave up on it.

I also tested the old coil. It provides no spark either.

Interesting is when I touched my multi-meter to the primary and secondary connectors on each coil, the new one reads around 7.5K ohms. The original coil reads around 4.0K ohms. Does that mean anything?

So in summary:

My test light pulsates when connected to the power wire going to the coil when cranked over. Spark plug fires on another engine.

Tried the original coil and original CDI ignition box and the new CDI ignition box and new coil to no avail.

Couple of thoughts.

1) The new coil this guy ordered was DOA.

2) If the polarities are reversed on the coil by accident, could this short the coil out?

If your wondering why I didn't use the coil off one of my bikes, well we were doing this at work! I tested the new spark plug on our gasoline powered warehouse sweeper. If I had thought, I would have pulled a coil off one of my parts bikes. Or the bike my co-worker gave me.

Any ideas?

FLASHLIGHTBOY · 10-25-2019, 11:26 AM

hello.... check youtube for how to do videos.... there are a lot of video.. I do not know why it is not posted in a sticky on here... how to check for spark.... check your stator for spark.... it is a easy test... ok 2 wires to check for ohms and voltage... the major thing is to always start at the CDI... check the kill wire... the black one witht he tracer.... see if it is grounded.... test light on positive... and touch it... if light comes on... then it is grounding your spark to not fire.... go from there.... you can remove the wire pin from the socket..ONLY,,, if it is grounding to try for spark then... see youtube…. then go from there..

turbofiat124 · 10-25-2019, 05:00 PM

Yeah, that's pretty much what I've done.

I just want to know if the 12V+ power wire feeding the coil is supposed to flash when checked with a test light when the engine is cranked over. That would indicate that the CDI is working. The kill wire going to the coil is disconnected so the coil should fire.

I just can't get the spark plug to fire when laid against the engine. Its a new plug but I tested it on our gas powered sweeper at work and I've got good spark when hooked up to a Kubota 3 cyl gas engine.

franque · 10-26-2019, 03:36 AM

This is a CDI kill wire that he's talking about though. Just check to see if that is grounded.

turbofiat124 · 10-26-2019, 07:48 AM

Quote:

Originally Posted by franque

This is a CDI kill wire that he's talking about though. Just check to see if that is grounded.

If this wire is disconnected from the coil , it should bypass any issues there might be with the kill switch.

10-25-2019, 06:07 AM	#1
turbofiat124 Join Date: Feb 2017 Location: Kingsport, TN Posts: 108	Troubleshooting CDI ignition. I'm trying to troubleshoot why a co-worker's Kymco 90 Mongoose has no spark. This is my first troubleshooting experience with a CDI ignition system. I've troubleshooted this bike for a couple of hours using the wiring diagram. There are two wires going to the coil. The black/yellow wire comes from the CDI and is connected to the black pin on the coil. When the engine is cranked over, using a test light, the test light pulsates when connected to the black/yellow wire. The green wire which goes to the green pin on the coil goes to the kill switch which finds it's way to ground when the switch is closed. At least that is the what the wiring diagram shows it. I disconnected it just to rule this out. This is how the kill wire works correct? Just like a lawnmower engine there is a ground wire coming off the coil. When grounded, it kills spark to the engine. On this ATV, this wire does the same thing, correct? Meaning if disconnected, the coil should still function. The coil itself is grounded through the mounting screw so this wire should have no other function. It is not necessary for the wire to be connected to the coil for it to actually function, correct? Does this make sense? When the spark plug is installed on another engine and checked for spark it fires. But when hooked to this coil does nothing. My co-worker said the bike just stopped running one day so he tried installing a new spark plug. He did not properly gap it but I did tonight. He had someone else work on it before me. I have no idea what this guy did but he tried installing a new CDI and a new coil but still couldn't get it to fire. He gave up on it. I also tested the old coil. It provides no spark either. Interesting is when I touched my multi-meter to the primary and secondary connectors on each coil, the new one reads around 7.5K ohms. The original coil reads around 4.0K ohms. Does that mean anything? So in summary: My test light pulsates when connected to the power wire going to the coil when cranked over. Spark plug fires on another engine. Tried the original coil and original CDI ignition box and the new CDI ignition box and new coil to no avail. Couple of thoughts. 1) The new coil this guy ordered was DOA. 2) If the polarities are reversed on the coil by accident, could this short the coil out? If your wondering why I didn't use the coil off one of my bikes, well we were doing this at work! I tested the new spark plug on our gasoline powered warehouse sweeper. If I had thought, I would have pulled a coil off one of my parts bikes. Or the bike my co-worker gave me. Any ideas? __________________ http://s222.photobucket.com/user/tur...?sort=2&page=0
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10-25-2019, 11:26 AM	#2
FLASHLIGHTBOY Join Date: May 2009 Location: SASKATOON Posts: 1,161	no spark hello.... check youtube for how to do videos.... there are a lot of video.. I do not know why it is not posted in a sticky on here... how to check for spark.... check your stator for spark.... it is a easy test... ok 2 wires to check for ohms and voltage... the major thing is to always start at the CDI... check the kill wire... the black one witht he tracer.... see if it is grounded.... test light on positive... and touch it... if light comes on... then it is grounding your spark to not fire.... go from there.... you can remove the wire pin from the socket..ONLY,,, if it is grounding to try for spark then... see youtube…. then go from there.. __________________ DEALER FOR ZSTAR & GIO PRODUCTS, TAOTAO ABIBABA ATV ETC
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10-25-2019, 05:00 PM	#3
turbofiat124 Join Date: Feb 2017 Location: Kingsport, TN Posts: 108	Yeah, that's pretty much what I've done. I just want to know if the 12V+ power wire feeding the coil is supposed to flash when checked with a test light when the engine is cranked over. That would indicate that the CDI is working. The kill wire going to the coil is disconnected so the coil should fire. I just can't get the spark plug to fire when laid against the engine. Its a new plug but I tested it on our gas powered sweeper at work and I've got good spark when hooked up to a Kubota 3 cyl gas engine. __________________ http://s222.photobucket.com/user/tur...?sort=2&page=0
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10-26-2019, 03:36 AM	#4
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	This is a CDI kill wire that he's talking about though. Just check to see if that is grounded.
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