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Discussion Starter · #1 ·
I’ve got a 2016 ktm sx250 in the workshop that someone has had a good f*#ck about with. My problem is no power from cdi to coil. The cdi is brand new and getting power when kicking over. Continuity tested in wire from cdi to coil and it’s fine. Any suggestions 🤷🏽‍♂️🤯

Ben
 

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If the CDI is getting power when kicked over (AC at around 10-15 volts if memory serves me correctly) and the CDI is brand new then I'd be looking at the trigger coil, is that in spec and do the wires actually make it all the way back to the CDI in terms of continuity. Also check that the kill switch wire is not reading continuity to ground, do this check where is actually goes into the CDI.

EDIT, I've just dug up the info for my EXC when I was trying to fix an ignition issue, it might help you with your issue, photo attached, your stator might not have the two yellow wires because your bike does not have lights, battery etc. The Red and White wires are the power from the stator to the CDI (They change colours at the connector!) The other Red and Green wires are the trigger wires that tell the CDI when to fire the plug. Also I don't think you have the grey loop wire which is to allow my bike to run in 'soft' (gay) mode.
 

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Discussion Starter · #3 ·
Yeah checked continuity of everything and all is good. If I kick it over a few times then put my test light onto wire going to coil it gives a little spark which makes me think output of stator is low
 

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Yeah checked continuity of everything and all is good. If I kick it over a few times then put my test light onto wire going to coil it gives a little spark which makes me think output of stator is low
If I was you I'd disconnect the stator from the CDI then attach a volt meter set to AC to the power output of the stator then kick the engine over, you need to see 10-15 volts AC.
 

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Discussion Starter · #5 ·
Will give it a go, thanks mate 👍🏽 Was told the stator was new, just looked and it’s definitely not! 😂
If I was you I'd disconnect the stator from the CDI then attach a volt meter set to AC to the power output of the stator then kick the engine over, you need to see 10-15 volts AC.
the voltage output of the stator gets to just under 6, you think this could cause zero power to the coil?
 

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Will give it a go, thanks mate 👍🏽 Was told the stator was new, just looked and it’s definitely not! 😂

the voltage output of the stator gets to just under 6, you think this could cause zero power to the coil?
OK, so the 10-15 Vac was a figure given to me by Trail Tech for their stator, having said that I am 99% sure that the Trail Tech stator should/would operate in the same way as the KTM one with regards to supplying power to the CDI, after all if their stator gave a hugely different power output to the CDI they could cause the CDI to fail which would not be good for their business!

The 6 volts you are getting does seem to be a bit in 'no-mans' land, it would have been cut and dry if you had said 2 volts!

Personally I am 75% sure that your stator is dodgy but it would be great if you (Or someone) could carry out the same test on a similar bike which has a KTM stator fitted. The system works by storing this charge in a capacitor and then 'dumping' it across the coil in order to fire the plug, 6 volts might be enough to get the CDI to power up and operate, i.e dump the voltage across the coil but the issue is that it is dumping a low voltage. I work with CDI systems on cars (fitting aftermarket systems) and they dump a large voltage on the primary side of the coil, 350 volts, so even a shock off the primary side of the coil will knock you off your feet! The KTM system might differ to a degree, of course.

Measure the resistance across the red and white wire with them disconnected from the CDI, they should read 18-20 ohms.

Where abouts are you based?
 
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I’d be inclined to test / replace any relays. Check test the regulator (Rocky Mountain atv has a great vid on this) & then double check the stator. If you need to go for a new regulator, go OE, ive just gone through a 500 exc & aside from checking the loom, switchgear, sensors front to back, back to front we found the regulator wasn’t allowing the switchgear to open up & let power through
 

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I’d be inclined to test / replace any relays. Check test the regulator (Rocky Mountain atv has a great vid on this) & then double check the stator. If you need to go for a new regulator, go OE, ive just gone through a 500 exc & aside from checking the loom, switchgear, sensors front to back, back to front we found the regulator wasn’t allowing the switchgear to open up & let power through
The ignition side of the wiring does not use and relays or rectifiers. AC is fed into the CDI unit, it is rectified 'internally' within the CDI. Post 2 in this thread shows the wiring diagram for a 300 EXC, it will be the same for the other 2 stroke KTM's, you can see that it is quite simple.
 

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Discussion Starter · #9 ·
So, got new stator with a stator plate and tdc pickup this morn and still no spark. It seems so power at all to the coil 🤷🏽‍♂️
 

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If I was you I'd be running continuity tests for all of the wires, do the wires from the connector that the stator plugs into actually read zero resistance at the plug that goes into the CDI, the wires that you need to be concerned about are the red and white wires that come from the stator, they supply the AC to the CDI, annoyingly the colours change at the loom connector, they go to a red wire with a white tracer and a black wire with a red tracer. You need to do the same thing with the trigger wires. You then need to do the same thing with the wire that leave s the CDI and goes to the coil, it should be zero resistance from one end of it to the other end. The kill switch wire must not be reading zero resistance between it and the chassis ground.

Just out of interest you could check the AC voltage from the stator when kicking the engine over (the AC voltage across the red and white wires).

I hope that the colours for the wires are the same as my EXC bike (as per the picture of the wiring diagram the I posted up!)

The only thing you haven't changed is the actual ignition coil, you can check the resistance of the two actual coils that are inside the the ignition coil, 0.5 ohms from the tab connector to the metal part of the coil and 6.37k ohms from the HT lead (cap removed) again to the metal part of the coil, also check that the coil has a good earth wire (brown) and has a good connection to the frame through the mounting bolts.
 

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Discussion Starter · #11 ·
Yeah I’ve tested continuity of every wire on the bike, all is fine. Previously did a resistance check on the coil, all in spec. I’m beginning to think the new cdi they gave me with the bike could possibly be faulty. There is power going to cdi, power coming out to kill switch but none to blue/white coil wire
 
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