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miyami 02-06-2020 12:17 AM

Ignition problem. One spark !
Hello Everybody.
This is my first post on this forum.

I am having an ignition problem on my 2005 Rebel CMX250C - CA model. Here is the story:

The bike would occasionally cut out at higher speeds on freeways, and then come back - which I thought was due to fuel problems. Then a couple weeks ago, it would not start after sitting for a couple of days. I thought I had problems with the Nanny wire and checked all wires and got the spark plugs out. Tested ignition, and could see one weak spark and then nothing. After checking some more wiring, I suspected a weak battery, jumped the bike with a car battery, and the bike started reluctantly. So I charged the old battery, and ordered a new battery for replacement. I could ride for a couple of days, and then the bike died on one morning after riding for 100m. I could not restart it, so I went back home, hooked it up to the car battery again, but nothing.
Meanwhile the new battery arrived. Hooked that one up, no spark. I checked the wiring to the CDI again and got the following results:
GRN - Ground
BLK/WHT - ground when either Ign switch is off, or run/stop switch is on stop // open circuit to start --> OK
BLK/RED (Ignition source) - 125 Ohms to Ground (spec says 270-340 Ohms)
BLU/YEL (pulse coil) - 111 Ohms to Ground (spec says 90-100 Ohms)
GRN/WHT (nanny wire) - GND with sidestand down & Transm in Neutral / GND with raised side stand / GND with Clutch pulled / Transm in gear = Open --> OK
BLK/YEL (firing wire) - 1.6 Ohm (spec says 0.1-0.2 Ohms)
Ignition coil 1: primary: 2.2 Ohm/secondary 14.4kOhm through plug cap
Ignition coil 2: primary: 2.3 Ohm/secondary 15.5kOhm through plug cap

Both spark plugs have no spark (tested with different spark plugs that worked before as well). The Ignition source seems low with 125 Ohms, but I saw a thread here that had the same value, so not sure there is something wrong with the exciter coil.
I suspected the CDI being bad, so I ordered a cheap replacement CDI (Onyx4u), which didn't work. Then I read that these cheap units often don't work, so I ordered another CDI from Rick's Motorcycle Electric (the Argentinian one), and tested it today. I got one weak first spark and then nothing - checked with a car battery again. So now I have probably 3 working CDIs, but still no spark. All wiring up to the stator connector looks ok.
Before I start taking the stator apart, I wanted to ask you guys, if anything of the above sounds familiar ? I am really scratching my head on this one.

SoakedKarma 02-06-2020 05:26 PM

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The battery has No influence on ignition spark system..
Rebel will run without a battery though is is hard on the voltage regulator/rectifier and could damage it..

Black/Red alternator exciter coils supplies a minimum of 100Vac to the CDI
The old spec is 270-340 ohms
Blue/Yellow pulse generator coil supplies spark trigger voltage minimum of 0.7Vac
old spec 0.1-0.2 ohms
Did you subtract your meter lead resistance from final readings?..
My leads have a resistance of 0.4 ohms all by themselves..

These ohm reading were very imprecise back in the day, have been replaced by peak voltage testing using an adapter attached to your digital multimeter.. Ohm readings can vary widely due to oxides or corrosion that can buildup on harness connectors..

The 96-2006 Honda Rebel oem shop manual testing page shown below gives the test voltages shown above..

In a pinch;
I would disconnect and reconnect the pulse and exciter coil connectors that are located just above where they exit the Left case cover in the hope doing so scrapes away oxide that may have formed causing high circuit resistance.. While disconnected you can retest ohm readings as well..

SoakedKarma 02-06-2020 05:53 PM

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Originally Posted by miyami (Post 1247415)
GRN/WHT (nanny wire) - GND with sidestand down & Transm in Neutral / GND with raised side stand / GND with Clutch pulled / Transm in gear = Open --> OK

Side stand Up should be a grounded circuit..
placing it down should cause an open ground..

2nd generation Honda oem repair manual is available on The wiring diagram at end of manual is for 85-87 1st generation Rebel and doesn't apply to your year bike..

miyami 02-07-2020 12:12 AM

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Thank you SoakedKarma.

I measured the output of the pulse generator and got 2.72V/-2.96V peak to peak (image1/measured at the harness connector).
And for the exciter coil I got ~100V peaks (image2/measured at the CDI - BLK/RED against common ground).
I suppose this looks normal even if it's right at the limit ?

Good catch with the meter lead resistance. They measure 2.2 Ohms when shorted.

With the side stand, I meant if I have the side stand down and transmission in Neutral, I get GND on the Nanny wire, which I believe is correct. I tested the side stand switch individually, and it is fine.

All of this looks normal to me except the resistance of the exciter coil. But still no spark. Is there anything else that comes to mind that is obvious to test ?

SoakedKarma 02-07-2020 03:45 AM

Nice grafting o-scope, what is it?
low resistance with minimum output would lend me to suspect exciter coil..

Frame grounding connection for wire harness pops into mind..
Harness ground wire lug is found bolted to frame above and slightly aft of coils..
pulling straws with that idea..

SoakedKarma 02-07-2020 04:04 AM

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The 2 large coils of the stator generate CDI voltage
I would expect to see a pattern reflecting a rise with bump higher as magnetic field passes past second coil..

miyami 02-08-2020 07:49 PM

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Is it possible to fry a CDI when measuring voltages on the ignition coil primary side without the coils attached (no load on CDI)?
I am getting weird results when measuring the voltage at the primary side of the ignition coils (GRN | BLK/YEL). The attached image is with the original CDI attached. If I use the two other new CDIs I am getting no reading at all. I understand that this should have 100V minimum peak as well (same as exciter coil output).
Again, this is done with the side stand up, nanny wire (GRN/WHT) = GND, BLK/WHT = open at CDI.

SoakedKarma 02-08-2020 09:01 PM

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danged if I know, anything is possible.
Very strange output signal though..
(GRN/WHT) = GND, BLK/WHT = open at CDI is correct in my book

below is a generic schematic of an AC Cdi to give you an idea what's inside

bweighmaster 02-11-2020 03:29 PM

Remove every component , clean all grounding contacts ... re install , run and check .... grounding of cdi , coil , stator , and pickup coil is most important ....

miyami 02-12-2020 11:41 PM

Are there any particular grounding points to look for other than the green wire at the CDI and at the ignition coils primary side ? I thought the rest is all grounded through chassis attachment screws (e.g. stator, spark plugs, etc.)?

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