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04 Rebel CMX250C
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Discussion Starter · #1 ·
I recently purchased a 04 CMX250C as a project. I cannot get any spark. I did not get any resistance reading thru my pickup coil so replaced it with a used on that has resistance. Manual says I should get 7 volts when cranking. I get 3. Do I need a new pickup coil? Stator seems fine all winding are equal and not grounded out. I understand that has nothing to do with spark, just mentioning it. I don't want to just replace stuff without a reason. Any help would be appreciated.

New to this forum, so if I did it wrong tell me
 

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1987 CMX250C AC
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1,883 Posts
You should be getting more than 100volts out of Exciter coil which supplies power to AC CDI

110321


Greater than 0.7 volts out of Pulse generator coil which triggers CDI to fire spark plugs..

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these measurements are made with Peak Voltage adapter attached to multimeter set to read DC or some (not all) fluke meters do it without adapter using RMS setting..
 

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1987 CMX250C AC
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before you replace any more parts I would check kick stand switch..

110323


With Ignition switch On,, CDI 2 wire connector unplugged check you Do Not have continuity from Black/White connector terminal to ground..

Green/White Circuit of 4 Wire CDI connector Should have Continuity to Ground when one of 3 conditions exist.
(1) Transmission in neutral
(2) Clutch handle pulled
(3) Kick stand in Up position
 
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1986 Honda CMX 450 Rebel
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26 Posts
Even after 42 years of repair & maintainance, i tend to forget the sidestand switch.
 

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04 Rebel CMX250C
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8 Posts
Discussion Starter · #5 ·
Thanks for the responses. But, I am getting older and can only handle one issue at a time. So I have a two wire harness coming from impulse coil. I read 120 ohms across the two wires. It is still unplugged from bike so I should be eliminating any safety switches. With my meter neg. lead grounded at battery and pos.lead on blue/white wire I crank engine. No Reading for voltage! I tried neg. lead on Green/white wire and pos. lead on Blue/white. Crank engine-nothing! I should be getting some kind of trigger voltage...shouldn't I???
The Black/red wire that plugs into CDI reads 120volts when cranking.

That is as far as my brain will handle at the moment. What do you guys think?
 

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04 Rebel CMX250C
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8 Posts
Discussion Starter · #6 ·
Thanks for the responses. But, I am getting older and can only handle one issue at a time. So I have a two wire harness coming from impulse coil. I read 120 ohms across the two wires. It is still unplugged from bike so I should be eliminating any safety switches. With my meter neg. lead grounded at battery and pos.lead on blue/white wire I crank engine. No Reading for voltage! I tried neg. lead on Green/white wire and pos. lead on Blue/white. Crank engine-nothing! I should be getting some kind of trigger voltage...shouldn't I???
The Black/red wire that plugs into CDI reads 120volts when cranking.

That is as far as my brain will handle at the moment. What do you guys think?
In Laymans terms...what does the Peak Voltage Adaptor do?
 

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1987 CMX250C AC
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Peak Voltage is the measurement of cycles Alternating Current voltage peaks..

Not surprising to me the momentary activation of Pulse generator coil isn't producing a voltage reading..
I assumed you had peak voltage capable meter when you indicated 3 volt output of pulse/trigger generator..

an Adapter or RMS capable meter is needed to latch on the momentary peak of each AC cycle..
Standard Analog or Digital multimeter tend to give an average of voltage output nor are they fast enough to catch peak voltage..

110334


1st generation Rebel measured Pulse generator ohms.. Specs are 90-100 Ω,, You indicate 120 Ω which wouldn't concern me much even though a bit high.. My meter leads alone add 4 Ω to any readings I do..
I'd make that test at two prong connector connecting between Blue/Yellow and Green/White wires in that connector..

Exciter coil of 1st gen Specs are 270-340 Ω,, But the 1st gen only has 1 coil compared to two of 2nd 96-2016 gen..
The single Black/Red wire connects to two large Exciter coils attached to stator.. Exciter peak voltage output can be tested between the connector and frame ground..

The Three Yellow wires provide three phase AC current to voltage regulator which is converted to DC..

Check stand switch by unplugging 4 wire CDI connector, testing that Green/White is grounded while transmission is in any gear other than neutral.. if grounded place stand down, now pull clutch handle, again you should see grounding of circuit.. Finally with stand down clutch handle released place in neutral, should see grounding of green/white circuit again.. All three safety systems are checked..
 

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04 Rebel CMX250C
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8 Posts
Discussion Starter · #8 ·
Peak Voltage is the measurement of cycles Alternating Current voltage peaks..

Not surprising to me the momentary activation of Pulse generator coil isn't producing a voltage reading..
I assumed you had peak voltage capable meter when you indicated 3 volt output of pulse/trigger generator..

an Adapter or RMS capable meter is needed to latch on the momentary peak of each AC cycle..
Standard Analog or Digital multimeter tend to give an average of voltage output nor are they fast enough to catch peak voltage..

View attachment 110334

1st generation Rebel measured Pulse generator ohms.. Specs are 90-100 Ω,, You indicate 120 Ω which wouldn't concern me much even though a bit high.. My meter leads alone add 4 Ω to any readings I do..
I'd make that test at two prong connector connecting between Blue/Yellow and Green/White wires in that connector..

Exciter coil of 1st gen Specs are 270-340 Ω,, But the 1st gen only has 1 coil compared to two of 2nd 96-2016 gen..
The single Black/Red wire connects to two large Exciter coils attached to stator.. Exciter peak voltage output can be tested between the connector and frame ground..

The Three Yellow wires provide three phase AC current to voltage regulator which is converted to DC..

Check stand switch by unplugging 4 wire CDI connector, testing that Green/White is grounded while transmission is in any gear other than neutral.. if grounded place stand down, now pull clutch handle, again you should see grounding of circuit.. Finally with stand down clutch handle released place in neutral, should see grounding of green/white circuit again.. All three safety systems are checked..
 

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04 Rebel CMX250C
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Discussion Starter · #9 ·
OK, Seriously I am having thinking difficulty at "70" so bear with me. I did the safety test and I am pretty sure the stand switch is working, but don't understand the clutch part. Here are my results: Stand down, trans in Neutral=no ground.
Stand up, trans in neutral=ground. Stand down, trans in or out=no ground. Stand down, trans in or out, squeeze clutch=no ground. I don't see any switches related to the clutch! I see it in the diagram but where is it on the bike?
It looks like the solid green wire at the 4pn connecter should be reading a steading ground? Mine is not. Problem?
Really appreciate your help. I am going to try a working CDI tomorrow I think.
 

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1987 CMX250C AC
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Clutch switch fits into bore cast in clutch handle/mirror mount
you can see electrical blade connectors peeking out in image

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110354


sounds like your side stand switch is working properly from your testing results..
 

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1987 CMX250C AC
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1,883 Posts
at this point i'd check the resistance of Exciter coil, checking between Black/Red stator connector and engine case which is ground..

We know your pulse generator coil is 120 ohms already
 

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04 Rebel CMX250C
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Discussion Starter · #12 ·
I see it now, thought that was related to turn signals. What did you think about the solid green wire next to the green/white. Is it a full time ground, like it shows in diagram? Mine does not show a ground.
 

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1987 CMX250C AC
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solid Green is connected to frame as full time ground

Green/White interconnects CDI (ignition control module) to Neutral and Side stand safety switch, grounding points, as well as functioning as starter relay ground..

it's within this Green/White circuit the two diode assembly comes into play separating dual use of neutral & side stand switches grounding points from Starter Relay and CDI common ground usage..

110356
 

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1987 CMX250C AC
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for 2nd gen Rebel I use wiring diagram found on internet as the pdf Honda shop manual I have has the wrong wire diagram.. I manipulate the diagram to fit the occasion..
below is full unmolested diagram

110358
 

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04 Rebel CMX250C
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Discussion Starter · #16 ·
What I down loaded is blurry and I can't read the writing . Well, today was a success! I purchased a used CDI and she fired right up. It has been a learning curve that I am glad to have experienced. I now have a much better understanding of the ignition system. From a no start I have found one bad spark pug end, one bad pickup coil, and lastly the CDI. I was told from the beginning to replace the CDI. But glad I did it step by step. I really appreciate your and everyone else in the advice and tech input.
 

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1987 CMX250C AC
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1,883 Posts
I have learned a lot from other members here myself
Happy it has worked out for you.........

There are reliable New aftermarket CDIs for sale should one be needed..
those marked IHA6008 either from Argentina or China perform the same as Honda branded..
 
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