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I recently purchased a 1990 250 MX as a project it seemed to be a real solid place to start as the bike was complete and mechanically it looked intact (good compression, things are supposed to move moved and things that arent didnt . The previous owner alerted me to the fact that there was no spark which I figured could only be the stator CDI or coil and given the price of the bike I have some money to put into it but I would like to figure out why it's acting the way it does rather than pouring $500 into it right off the bat on a new ignition system.

Now to what I have found digging into it.
Stator: SEM Type KC on the left side of the motor. 4 wires, 2 light blue (coming from the sealed windings), 1 black and 1 green (coming from the crank position pickup)

I pulled the flywheel and stator, cleaned and ran new wires, solder, heat shrink, the works, up to the cdi (the old ones were nicked badly by the previous owner when he cut the wrap off them). Checked the resistances Green to Black was 168 Ohms which is real close to spec being 170 Ohms, Blue to Blue was 16.2 which is also close to the specced 16 Ohms.

CDI: Dont know a ton about this as it's kinda the sealed black box of the whole system... Power/Signal should go in and come out. The strange part is that the connectors for the CDI from the stator are Light Blue, Red, Green, Black. The previous owner had one of the light blue's on the stator going to the red wire on the CDI. Is this correct? The CDI has 2 blacks and a green on the output plug, what should I expect from these in the correct wiring scenario? Given different wiring configurations I have seen a "Digital like pulse" leaving the CDI as well as what appears to be strong power on the test ligth, never both which is what I presume it needs. Ideas?

Coil: The previous owner replaced the coil and when that didn't solve the problem he gave up and sold it to me. 3 wire input White, Red, brown (signal, power, ground)? It also has the orange kill switch wire which i presume needs to be open rather than connected to ground.

Here's the fun part. at one point I switched the 2 light blue wires going in to the CDI from the stator, I got a single set of sparks which I presumed was the CDI doing its job, but then I couldnt reproduce it for about five minutes and all of a sudden it did it again 2-3 solid strong blue sparks. It seems to me like the CDI is only doing half its job depending on the wiring, one configuration charges the capacitors, and when I switch them it recieves the signal to discharge. I dont understand how switching the blues (unconfirmed as the cause) could affect the crank position sensor, those were notably the Green and Black wires from the stator.

Anything would help. I am flying blind at this point. Thanks in advance,
Ben
 

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I recently purchased a 1990 250 MX as a project it seemed to be a real solid place to start as the bike was complete and mechanically it looked intact (good compression, things are supposed to move moved and things that arent didnt . The previous owner alerted me to the fact that there was no spark which I figured could only be the stator CDI or coil and given the price of the bike I have some money to put into it but I would like to figure out why it's acting the way it does rather than pouring $500 into it right off the bat on a new ignition system.

Now to what I have found digging into it.
Stator: SEM Type KC on the left side of the motor. 4 wires, 2 light blue (coming from the sealed windings), 1 black and 1 green (coming from the crank position pickup)

I pulled the flywheel and stator, cleaned and ran new wires, solder, heat shrink, the works, up to the cdi (the old ones were nicked badly by the previous owner when he cut the wrap off them). Checked the resistances Green to Black was 168 Ohms which is real close to spec being 170 Ohms, Blue to Blue was 16.2 which is also close to the specced 16 Ohms.

CDI: Dont know a ton about this as it's kinda the sealed black box of the whole system... Power/Signal should go in and come out. The strange part is that the connectors for the CDI from the stator are Light Blue, Red, Green, Black. The previous owner had one of the light blue's on the stator going to the red wire on the CDI. Is this correct? The CDI has 2 blacks and a green on the output plug, what should I expect from these in the correct wiring scenario? Given different wiring configurations I have seen a "Digital like pulse" leaving the CDI as well as what appears to be strong power on the test ligth, never both which is what I presume it needs. Ideas?

Coil: The previous owner replaced the coil and when that didn't solve the problem he gave up and sold it to me. 3 wire input White, Red, brown (signal, power, ground)? It also has the orange kill switch wire which i presume needs to be open rather than connected to ground.

Here's the fun part. at one point I switched the 2 light blue wires going in to the CDI from the stator, I got a single set of sparks which I presumed was the CDI doing its job, but then I couldnt reproduce it for about five minutes and all of a sudden it did it again 2-3 solid strong blue sparks. It seems to me like the CDI is only doing half its job depending on the wiring, one configuration charges the capacitors, and when I switch them it recieves the signal to discharge. I dont understand how switching the blues (unconfirmed as the cause) could affect the crank position sensor, those were notably the Green and Black wires from the stator.

Anything would help. I am flying blind at this point. Thanks in advance,
Ben
In your satator cover do you have a pick up trigger switch ? look and see if the magnet broke off ...or chreck this out......remove your kill switch then see if you have spark....the simptons just explained happened to my 250....i removed the kill switch and had perfect spark....bad kill switch was the problem......make all colors match....he was guessing
 

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Discussion Starter #3
In your satator cover do you have a pick up trigger switch ? look and see if the magnet broke off ...or chreck this out......remove your kill switch then see if you have spark....the simptons just explained happened to my 250....i removed the kill switch and had perfect spark....bad kill switch was the problem......make all colors match....he was guessing
No kill switch on the bike, not entirely sure what you mean by pickup sqitch there is a magnetic pick up for the magnet on the flywheel both are present and intact as far as I can tell. I ordered a used CDI on ebay that will hopefully come in sometime this week.
 

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No kill switch on the bike, not entirely sure what you mean by pickup sqitch there is a magnetic pick up for the magnet on the flywheel both are present and intact as far as I can tell. I ordered a used CDI on ebay that will hopefully come in sometime this week.
No kill switch ? how do you turn it off in emergency ?
 

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Yes blue to blue ..should be 28 - 32 or more volts just a guess though being theres no info on them....just looked on ebay and saw you have the small cdi....they have one for 99 bucks on ebay
The cdi that comes up on ebay here I think is for the 125 only the CDI on the bike looks like this

I ordered one this last weekend that the seller claimed worked, not sure how he could test it, but we'll see. Thanks for the numbers on the voltage ill check it when I get home and let you know.
 

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Yes blue to blue ..should be 28 - 32 or more volts just a guess though being theres no info on them....just looked on ebay and saw you have the small cdi....they have one for 99 bucks on ebay
I dont have a peak capable meter but Blue to Blue the highest I saw was around 10v AC... Seems a bit low, ill see if I can dig up a spec for it but I know when i checked the resistance it was right on so I wonder what could be affecting the voltage in those sealed coils?
 

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Brand new ngk 9 series.
I was looking at what the guy i bought my bike from said to me he got 47 volts from the 2 blue wires .....pull the plug hook your VOM to the 2 blue wires ....put the bike on a stand and have someone turn the back wheel...better then kick starting....let me know your voltage
 

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Discussion Starter #17
I was looking at what the guy i bought my bike from said to me he got 47 volts from the 2 blue wires .....pull the plug hook your VOM to the 2 blue wires ....put the bike on a stand and have someone turn the back wheel...better then kick starting....let me know your voltage
How fast does the wheel need to spinto get optimum voltage?
 

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How fast does the wheel need to spinto get optimum voltage?
anything is better then the kickstart...your just trying to see if you get more then the 10 volts you got from your reading ....i would say anything over 22-24 volts should be fine to achive a worthy spark.....make sure all black ground wires are clean and the spot they ground to are clean as well.......i would rather fix your bike then mine lets trade .....mines a mess from the last guy who owned it..... he was a real chopman go to youtube and look up" KTM needs parts" leave a comment to let me know you saw it
 

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Discussion Starter #19
anything is better then the kickstart...your just trying to see if you get more then the 10 volts you got from your reading ....i would say anything over 22-24 volts should be fine to achive a worthy spark.....make sure all black ground are clean and the spot they ground to are clean as well.......i would rather fix your bike then mine lets trade .....mines a mess from the last guy who owned it..... he was a real chopman go to youtube and look up" KTM needs parts" leave a comment to let me know you saw it
Saw your video, not really looking to trade at this point, new CDI came getting much stronger output good consistent 5v DC out both the red and green leads, the amperage readings on the 200m setting I get around 1.0 and .05 i dont remember which is which. this cdi hashas the ground strap on the plug, which when I plug it in to the coil all the power seems to be getting dumped back through that black wire so I'm thinking its the wrong coil.
 

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Discussion Starter #20
Maybe pictures will help

So I thought maybe some pictures would help spur some responses.

The year of manufacture on the sticker says 89 but it has the exhaust setup from what I think is a 90.

The CDI and Coil that were on the bike when I purchased it: I only get 5v DC out of the green wire 1 of the goes to ground and I cant seem to get anything out of the other black. Doesnt match any diagrams I have seen, yet to see one like this for sale, seemingly the ground passes through the cdi then to ground rather than straight off the plug.



A new (old) CDI that I bought, I think it is out of an 86, it has the correct wire colors leading in from the stator and matches the diagrams that I have found with the ground lead coming right off the plug. I get 5v dc on both the red and green leads. DC Amperage readings on the 200m setting are around 1.0 and .05



Any comments would be much appreciated.

-Ben
 
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