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My Electrical Problem Findings, 83 Honda CM250C


Jul 27, 2023
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Newfoundland Canada
looking for a cdi unit and a a/c generator/stator/magneto/alternator, this bike is hard to find parts for as it was only made for a few years, and my specific one was only made for 1 year. i believe that the rebel shares some but i need to confim that
Before jumping into the interchange rabbit hole your ignition needs a thorough diagnosis to see what the actual problem is. It could be as simple as a broken wire. The FSM has tests you can use for the diagnosis. A digital VOM will work in place of the special Honda analog VOM.
The flywheel is shared between the 250C and the Rebel CMX250 thru 1987.
The stator is 250C only. 1982/83
The coil is 250C only.
The CDI is 250C only.
The left crankcase cover appears to be shared with the CMX250 thru 2015.
The further I dig on parts fiches the deeper it gets. Looks like the CB250 Nighthawk shares pieces as well.
This is a crank fire wasted spark CDI ignition.
Looks like Honda was continually upgrading the ignition system. To use the later components is going to mean using the wiring harness from the later or making a ignition harness, probably easiest to make the harness.
no conclusions jumped, i have a video done up about it and ill do a write up too, the fsm i received this morning helped me get to my conclusion.
I bought this bike with electrical issues,but this is crazy, All lights,horn,switches,no breaks in wires,flasher,fuses,starter,starter solinoid,silcone rectifier,battery,pulse generator,grounds,clutch safety,neutral safety,ign switch,starter button works and is fine,it wasnt till this morning i recieved the FSM and found my issues,and boy are they big. attached is my paper work findings.The cdi ,coil and stator are dead. no continuity on charging coil,white and ground on exciter coil is null, white and blue at 822 ohms. And youll see on my cdi list findings whatts wrong with that.

MY harness.jpg Cdi Sheet.jpg
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didnt know i could do that, thanks

Of course, though it's something Jim or I would have to do for you. When working on the same bike for similar issues in the same category, it's always best to keep things in one place for the learning experience it may be for future readers.
The tests will be different with a digital meter. You need an analog meter with a fresh battery to bench test the CDI.

This is mostly a waste though, I have found that using a PVA/Peak Voltage Adapter is a more meaningful test. It can show you, dynamically, if it is generating voltage from the stator. Subsequently, you can use it to verify output from the CDI to ignition coil.

I have notes that someone gave me a long time ago that says the CB250T/CB250N/CM250T use the same circuit as the CM400A CDI. The only difference is that it does not have the SCRs for the 7.5 degree neutral timing, instead it is fixed at 15 degrees at idle. If this is true, and they mount the same then you can use a CM400T stator and CDI if yours are truly defective. Give use a picture of your stator attached to the bike and some measurements and I can find out if the fitment is the same. The CM400T is just fixed 15 degrees at idle, but the rest of it is essentially the same.
PS: If you do the swap and it works I am willing to buy your defective CDI in order to reverse engineer it... or at the very least it's likely possible to make an adapter from the CM400A CDIs.
OK. Based on some simple research it looks very likely that the whole CDI assembly is essentially the 400A. The outer part of the stator has the same kind of marks for the excitor coil and the pulser coil. My guess is they used the 400A design because it was available and it worked and just don't use the additional part of the circuit. The CDI appears to be the same except the removed the wires for the 7.5 degree/change relay. And then for the 250Cs they simplified it further to have it be a "plug in" unit instead of the 6-pin and 2-pin canon plugs.

The 400A stators and rotors are hard to find. But the 400T will mount up exactly the same. You'll likely have to come up with a mounting solution for the CDI itself. I have no idea how the grommet will fit, if it fits.

Get measurements of the rotor and stator. Thread pitch and bolt length of the rotor bolt. Measurements of the distance between the two screws for mounting the pulser coil also.

It seems like it should fit, and that it probably works. But I have never tried it. It's a shame you're so far away in CAN or I'd ship you a spare with a prototype CDI to test if it works. If that's something, after measurements, you want to try and are willing to pay a "core" and shipping both ways at your expense we can arrange that.
Just disconnect the kill switch and see if you get spark. Alternatively, cut one of the two wires running to it or extract the terminal from the canon plug with a pick tool/tiny flat head.

This seems correct to me, on OFF it's shorted which will complete the circuit to have the SCR output redirect to ground. When it's ON that circuit is not completed. Your kill switch works.

You need to get a Peak Voltage Adapter. You will be chasing your tail otherwise. I used to believe in DVM/AVM readings, but it means nothing if it benches OK but cannot hold up in circuit.

You are also doing the test wrong. You have in diode mode. It must be in resistance mode. Set it to the 200 ohm setting.
Another thing I have noticed is that I have seen a rash of stators recently where the low RPM coil windings are open. On the CM400s this is White to Green/Ground. I can't answer why this is. It's possible, but I do not guarantee this it is at your own risk... To swap the blue and white by extracting the canon plugs. It may get it to fire, but your RPM will probably be limited and it will run poorly... but it will tell you what's going on.

Either way, a PVA will make it totally obvious if the voltage from the low and high RPM coils are not generating, or the advancer coil or the pulser coil. If all of those are outputting voltage (sorry I don't know what the target spec is... but from the 400s it's about 200V for each coil... give or take ~75 VAC) and the advancer and pulser are generating some kind of voltage (I believe it should be anywhere from 0.1 to 1.0V, you just want it do something) then you can test the OUTPUT of the CDI by attaching one of the PVA probes to where it goes to the coil. I don't know what the colour is on your bike, but 400s it's a two pin canon plug that has a yellow and a green. Just attach the probes to both. You should get some kind of voltage. On the 400s it's quite low, about 0.7-1.0V when read from a PVA.

You can't use a DVM from these tests as the AC generated is happening so fast a DVM can't dampen it enough to do it. An AVM will work, but the readings will be different. The PVAs have a capacitor and resistor in circuit to help "collect" the peak voltage for a small amount of time and that influences the final output shown on your DVM.

Alternatively, you can use an oscilloscope, but I doubt anyone in the modern age has one and they're expensive to acquire a decent one. It's also annoying to use the probes on a scope. Just get the cheap PVA and report back on your findings. Get us measurements of rotor, stator, and mounting points for the pulser coil.
Sorry for multiple posts. My mind works too damn fast and I write things and then reflect right after.

You say the pulser coil and white to ground are reading open. This indicates to me that you MAY be lucky that the grounding eyelet is not attached or is corroded on the stator. Check it carefully. Clean it up and things may magically start working. Otherwise, the main part of the stator winding where it IS attached to the metal on the stator is open. And no, you can't fix it by yourself because you have to remove the enamel and unwind the whole thing. A lot of work, you need to count windings and where it crosses. After that you must use the correct epoxy, the same kind that is used to seal electric motor windings. This isn't something a homebrew person can do because the epoxy requires being baked off. If you find that you want to keep your original components and want to rewind your stator professionally DON'T use Rick's. Use Custom Rewind in Alabama. He usually has cores ready to go so down time is minimal. He also uses the correct epoxy and technique. Rick's doesn't and I hear lot's of stories where they fail within a year or two, sometimes almost immediately.
i did and still nothing because of my other issues, i mentioned in the other video that someone tried to bypass it and still wouldnt work, just odd that it says there shouldnt be any with ign on and kill in either off mode, im not concerned ,but when i get a cdi and stator and find those work and still no spark then ill bypass it again and see
Unfortunately everything is slightly larger, including the mounting holes with the 400 series.

You're going to have get the PVA and see if it's the CDI or the stator. If it's the CDI a 400T might work with adapting wires, though I do not guarantee it.
i did and still nothing because of my other issues, i mentioned in the other video that someone tried to bypass it and still wouldnt work, just odd that it says there shouldnt be any with ign on and kill in either off mode, im not concerned ,but when i get a cdi and stator and find those work and still no spark then ill bypass it again and see

I don't know what you mean. The test is simple, put it in resistance mode at 200 ohms on your DVM. Disconnect the kill switch from the CDI. In ON it should inifinity. In OFF it should read shorted/0 ohms.
To show you how to test. On the 400s there is a green wire and black w/ white tracer wire coming off the actual kill switch. You will see on the underside of the switch the two colours that come off it. Insert probes, set DVM to 200 ohms. It should read infinity when ON, ~0.0 ohms when OFF.

Physically remove the switch, inspect colours, and disconnect it from the CDI and wherever else it leads.

20230729_125953.jpg 20230729_125959.jpg
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It appears, upon studying your wiring diagram the colours are the same. So measure the killswitch out of circuit. Just disconnect the 8-pin canon plug (probably in the head lamp assembly) and test there. If good, now plug it in, disconnect the CDI canon plugs and test Black w/ White and Green via back-probing (the method I show in the picture). If it fails there then something is shorted and you have to find out where.

There is also a Black w/ White that runs from the key switch to the opposing 8-pin canon plug. Disconnect that canon plug and test the same way. It's possible one (or both) of these switches have dirty contacts.

If you don't care about any of this, just extract Black w/ white from the CDI canon plug or cut it.

The 1.7 ohms frame ground, if true, is bad. This means there is a corroded connector somewhere and you need to do a voltage drop test to find. You are saying 89.6 (?) ohms from Red w/ White from bullet to canon plug for fuse box? If yes, this is also bad and you need to voltage drop test it to find where it is.
The voltage drop test is simple. To test the Red w/ White, put one probe on the POSITIVE post on the battery (the battery must be charged) and turn the key switch ON. Now put the other probe to the bullet connector where it leads to the fuse box. It should read about 0.0V. ANYTHING over 1.0V is a problem. This means the connector is corroded. Clean it up with some contact cleaner and test again. If you still can't get it below 0.0V then it needs trimmed back and a new connector crimped. Don't use crappy automotive crimps, and please don't hard solder it.

If good, now move to one end of the fuse, if it's still good then the other side. If one of the ends reads over 1.0V then it's likely either the fusebox wiring is corroded or the fuse holder.

If all good there, then move onto Red from the key switch. Again over 1.0V is no good. It's possible it may read this at the key switch. This means the inside is dirty, it must come apart to be cleaned. Be careful as there is ball bearing and spring it rides on.

You can also test the key switch this way in circuit. One probe to Red the other to Black (yes, black) it should read 0.0V. If not, the switch needs cleaned.

For your frame ground, put one probe on the NEGATIVE post of the battery and the other probe to the frame ground. Same rules apply, keep working backwards on the wiring diagram to find out where it finally reads less than 1.0V. That means the previous connector is the bad one that needs cleaned/repaired.
Last thing to bother you about. You can test White and Green from the stator a bit easier by back probing the White that comes out of the stator and putting the other on the exposed metal of the stator. If it's still reading infinity in 200 ohms mode then this is your problem and the stator needs rewound or source another one for your year or another year. They're probably all the same, just the plugs may be different between years so you'll have to make an adapter.

When you flip the stator over in your video at 47 seconds there is an eyelet connector to the left. This is the ground. If it's broken/faulty then it won't complete the circuit for the coils which may be your problem. I hope it's your problem as this is easy to fix.
yes i did that test, some where .04ohms, but there were 2-3 that were bouncing around from 15-123ohms,and thats when i knew before i had the fsm that was the issue, i hve another cdi on the way, and im going to test it first with the same meter and see how that one comes out of that test,if it passes then we know a 10$ meter is enough to diag electrics on these bikes and that the old cdi was indeed faulty. as for the stator, i have ordered one for just the cm250 motor from early 90s,it was 45$ so whatever, im taking a roll of the dice on it,i also have found a aftermarket oem style coil and even though i checked the recticfier and seems ok, i got another on the way aswell for a few bucks why not,if either or works, i got spares or i can swap meet it. i also checked that ground on the stator and the ring was firmly attached to the wire
A $10 DVM that is not auto ranging will cause the test to give you wild results on bench testing the CDI. Most readings will come up in the KOhms or MOhms setting. This is specifically why they want you to use an analog meter. The leads may need to be reversed on a DVM to get the correct readings despite what the table says.

Seriously, buy the $30 tool. It's a worthy addition to your toolbox and if you get another bike with faulty electronic ignition you can use it to diagnose things easier instead of chasing your tail and blindly buying parts. If you had a PVA you could simply backprobe white to green and blue to green during cranking and see if you have any voltage being generated. If you don't, then it's simple, the stator is broken. If you got voltage there, then you simply backprobe the excitor coil and pickup coils. If all voltage checks out there, then you backprobe output of CDI to ignition coil to ground. If no voltage there, then the CDI is hosed. If you DO have voltage there then the ignition coil is bad.

The PVA makes it way easier than relying on bench resistance tests. One of the reasons Honda stopped giving the values in their FSMs is that too many people do them wrong: they have the wrong range set on the meter, they have a low battery in the meter, it's difficult at first glance to decrypt the +/- of the table, readings could be different depending on temperature, the table is also quirky in that it specifies KOhms for one meter and Ohms for the other meter and if it's wrong then you will get wild results.

Test the eyelet to the green out of the stator for 0 ohms. Just because that eyelet looks good doesn't mean it's not broken or corroded somewhere in that wire.

Having readings "bounce around" when measuring the same two points indicates that the probes are not fully inserted and making good contact (harder than it appears when back probing sometimes), there is "wire strain", corrosion or you have cheap probes that are flimsy.

I hope your parts fix your issue.
im back from work,i brought the stator and cdi to work where i have a flute 27 2 to help me,found the ground problem on the stator and have purchased a dva
View attachment 23929View attachment 23930View attachment 23931View attachment 23932View attachment 23933
bellow is dva testing in order
View attachment 23934

This is pretty much what I've been saying the whole time as a critical area to test. But, glad you figured it out.

P.S. the videos are kind of long. Pictures work better.
You are doing the test wrong. PVA/DVA needs to be in Volts mode, not ohms. The Red probe needs to go to the far right to "V" for "Volts". Set your meter to 250V at the top right. I believe this is AC. Check your manual. Very cheap meters like yours usually have a table on the back of the unit that tell you the settings. You want VAC. Not VDC.

That coil looks to be aftermarket. If it is, highly likely it has problems. Looks like an eBay cheapie.

To test CDI to coil output, disconnect the coil because I think it could be wired wrong or may be junk and won't give us decent results. Put one probe (doesn't matter which) to yellow/black bullet connector. The other probe goes to green at the CDI or you can use a frame ground. Doesn't really matter which. When the meter is on, not cranking it should be showing 0.00V. During cranking it will (guessing, it's different for each bike) be around 1.0V. Basically, some kind of voltage is what we want to see. This means the CDI is outputting something.

Recheck the rest of your stator during cranking with the fixed settings on the meter.

I must add, your meter seems a bit confusing and it's confusing me and you. It may be worth buying a competent one to do these tests. You don't need to break the bank on a Fluke meter. Any general automotive meter will work. The first link is a generic $34 USD one. OTC makes great ones around $100, but they do have a more basic line which is more than enough for what you need at about $65 USD, second link. They rival Fluke quality meters that are double in price (sometimes triple). A worthy investment, in my opinion, for electronic diagnostics on any vehicle. These bikes are old, the harnesses have corrosion, and things get funny. You will return to using this tool again at some point.

i wasnt sure how to use the dva properly so thank you for the clarification, it makes more sense to me now, i do need a better meter for sure,but this is what i have right now.
left sheet it my proper dva readings, ive noticed that my wiring diagram and the cdi sheet says the pinning of the wires are diffrent.ive tried swapping the pins around but no change.
20230820_162335.jpg 20230819_182352.jpgfuse panel is fine
I saw in your videos there are automotive crimp connectors. This says to me someone has severely goofed with the wiring.

Your G/W is bad nomenclature. This made me think Green w/ White tracer. CDI is outputting nothing... but your White to Green showing no voltage and if your chart is correct with the ~600 ohms indicates something is wrong with the windings.

However, you are using a digital meter and I have no idea if you have the correct ranges set. The numbers will vary.

I thought you said you bought another stator and CDI assembly? Do these also not work?

If the replacement CDI doesn't work, then your problem is the stator, ignition coil, or you have a bad ground. There is a way to bench test these coils, but you need bits of wire and a car battery to do it.

Also, you don't blindly test the wiring... Here's how you do it with the PVA:

First, put the meter in 10 ohms mode. Check continuity from Green and Green w/ White. These are shared grounds. It should 0 ohms. Not infinity, not 2 ohms, but 0.0 ohms. If it reads over 0.9 ohms you have a problem with your grounds.

Second, with the meter still in 10 ohms mode. Check continuity from Green to a frame ground. This can be a clean bolt on the engine, the engine mounts, the handle bars, kickstarter lever (if equipped). If you cannot find 0 ohms at any of these spots and they all read infinity then there is a ground problem somewhere. If there is, we may be able to "hack" around this temporarily until we can find out why.

Third, you are using the PVA wrong. Here is what you do:

Insert one probe to BLUE w/ Yellow and other probe to Ground/Green. This is the pulser coil. Crank. It should read some voltage.
Insert one probe to White and other probe to Ground/Green. This is one of the RPM coils (Low or High, unsure). Crank. Again, voltage.
Insert one probe to Blue and other probe to Ground/Green. This is one of the RPM coils (Low or High, unsure). Crank. Again, voltage.
Insert one probe to BLACK w/ Yellow and other probe to Ground/Green. This is the output of the CDI to ignition coil. Crank. It should read voltage.

If all these are reading voltage your problem is the ignition coil. If it is then refer to this thread on how to make an ignition coil tester: https://www.vintagehondatwins.com/forums/showthread.php?8342-DIY-Coil-Tester-Schematic.
PS: Ignore that chart. All it's doing is causing headaches. It may or may not be accurate to test the CDI because it relied on tests with an analog meter. Readings will vary depending on meter used, if it has a good battery, and ambient temperature.
I see you reading this thread. For you, I made a video of how I do the PVA test on a CM400A. The concept is the same, even some of the wiring.

It's still uploading and should be available in about 10 minutes. Hopefully this reduces confusion for you.

yes i have a spare cdi and results across the board are the same, the stator was for a honda cb250 92-00 and nighthawk 91-08, it was 40$ and hoped it fit but no, its slightly larger then the cm250 stator and wont fit in the flywheel. the new coil was bench tested on primary and secondary leads and everything is ok there.i have that cheaper multimeter on the way and just finished up the new readings
yes i have a spare cdi and results across the board are the same, the stator was for a honda cb250 92-00 and nighthawk 91-08, it was 40$ and hoped it fit but no, its slightly larger then the cm250 stator and wont fit in the flywheel. the new coil was bench tested on primary and secondary leads and everything is ok there.i have that cheaper multimeter on the way and just finished up the new readings
View attachment 24011

Does 000 indicate infinity or 0.00 ohms or 0VAC? You have a problem with white to green, which is your low RPM coil. The PVA, if done correctly the way I show you in the video, will verify if it's not putting out any voltage. I suspect it is not, the low RPM is needed to work at cranking or it will never spark.

Also, you're still doing the test wrong if these are ohm values. Stop doing resistance tests. Throw it out. Don't think about it. Use the PVA, only use it VOLTAGE mode. Give me voltage numbers. Resistance tests are not helping you. Watch that video.

If White to Green is still showing 0VAC, then yes. Your stator has a problem. The white winding is open. Your options are to find another from the same year or send it out to Kirk at Custom Rewind in Alabama. Do not use Rick's Stator. They don't use the correct epoxy for sealing the windings and they fail. This would also explain why CDI output to coil is reading 0VAC. If there's no low RPM voltage in, it can't put any out.

As a hack, after you have verified white to green is hosed, swap blue and white by extracting the pin connectors or soldering something up. The bike will likely start. It won't run well, but should start or at least spark.
the Direct voltage adapted is plugged in how you said,middle and right leads, then the meter is on alt current at 250.so the values your seeing are vac, ive tired looking for a new stator as i believed for a while this was the issue, but no luck,this stator was only used in this bike far as i can tell
0VAC out of white to ground is a problem. Considering blue to ground generates voltage and you have tested continuity from green to frame grounds this means the winding is opened for white.

Fixing this isn't a DIY task. Call Kirk at Custom Rewind, 1-205-798-7282, tell him what you have and tell him that the low rpm coil is open. I don't know if this bike was easily available in the US so he may not have any cores in stock. Otherwise, he usually keeps cores on hand ready to ship out so downtime is minimal. Price will likely be somewhere around $250-$300. It sucks, but you cannot get these anywhere else.

Someone before you likely tried replacing coil and CDI and had no spark, started goofing with wires, and gave up on it. This is why the PVA is way better than relying on resistance tests. It shows you, dynamically, while trying to do things in circuit if it's actually working.

So yeah, unfortunately you will have to find another one, but it sounds doubtful... or just have Kirk rewind it. Only use him, I do not recommend anyone else. He's cheaper, and he's also been doing it since the 1980s and does it the correct way. Everyone else uses air curing epoxy which is inappropriate for these stators.
And while you're at it... determine if that coil is aftermarket. With the weird pigtail I believe it is.

Look in the book see if it has resistance values for the primary ignition coil. Let me know what it is, very likely 0.5 ohms. If so, you are in luck as Dynatek makes a great one. These no-name aftermarket coils are terrible. I've seen them read way over spec, like 5+ ohms and the readings vary wildly indicating poor quality materials. If the bike will start on it, they cut at after the bike warms up and it runs funny. Don't waste your time on those coils.
That's the same junk one you essentially have now.

Get a Dynatek DC11-2 since you confirmed it's 0.5ohm. This is a high quality coil. Not some cheap junk. Any coil that is $20-$30 is a piece of junk waiting to fail on you at any moment. Believe me, I speak from experience on this.

EDIT: That coil looks suspiciously similar to the one I pulled out of a CM400A for a customer recently. Total piece of trash. Was reading 5 ohm, then 2 ohm, then 8 ohm non stop. Really terrible quality with terrible crimps and thin wire gauges. The caps were also poor quality and loose on the plugs.
There is no guarantee that will work, sometimes it works on some bikes not on others. VAC to trigger the SCR may be different. Either way, you need the stator rewound. Anything else you do at this point is useless.
The AC-CDI's are troublesome to diagnose.
Check your rotor sensor reads some ohms like a coil(100-200 ohms typical), one end should go
to ground. Check the spacing it detects on rotor, closer generally better.
The AC-CDI is powered by AC from rotor coil(typically 200-400 ohms typically), one end again
will be to ground.

A suggestion, get yourself a $12 or so discount DC-CDI, like this one:

Google on the wiring, hook it up on the bench with 12v.
Make spark. To fake a input signal you can use a small cap(like 0.1uf bypass cap) or a
resistor like 1k or 100k to the input wire, and just brush the other end with 12v and that
should generate a spark.

After you know you can make a spark, you could try your coil with it, or try your input
sensor with it, or get your engine running on it.

The DC-CDI bypasses the stator high voltage required for the AC-CDI.
You can also pick up discount $10 AC-CDI's that can be useful for troubleshooting.
Now these things can get weird and interesting to do advance and all, but hopefully
this can help troubleshoot.
heres an update, i called around my local shops and no one can fix the stator,i looked online and msged many people for a used one, no luck, so thanks to somone in the comments i got in contact with Kirk from custom rewind in Alabama, spent a good while talking to him about the bike and what ive diag and gave him whatever information he needed, i had it all, the man so nicely looked in his bone yard with no avail. BUT, he has the info from years ago to be able to rebuild it! so September 5th i had put that in the mail to him which is 44hrs or 2500Miles away from me. next update wont be till i get it back to me
last update on 83 Cm250 Custom, custom rewind had fixed the stator,there was a broken wire in the low rpm coil, along with his southern hospitality that man graciously gave my a stator form a 250 rebel which is exacly the same, i cannot remember the year he said it was.Then the oem cdi was toast so i got a new one and still couldnt get it to the coil, while waiting for a used good working condition coil to come in from england a local man 20mins away had msged me about the bike, and was willing to trade the bike as is for a working and running
81 Honda GL500 Silverwing, after seeing a few pictures and vides of his and me sending pics and vids to him, i really liked the the silverwing more, so we did the trade yesterday, this is how i dropped off the bike, this guy had two other cm250s, his plans for this one is to do an old GP racer with fearing. Tonight he sent me these 3 short videos
vid 1-
vid 2-
vid 3-

The coil was fine, but the harness was the issue. he had a spare parts bike and tried it and boom running cm250, he will be sending me updates on his build, i was very happy it went to someone who could get it running again and very stoked to see his build. thank you all for your help and information and knowledge. dont let the old stuff die

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