KTM 250sx kills spark plugs, not foul.. totally breaks them...

[Dirtbiker227]

Hey guys been a while since I posted on here as I stopped riding for a while. Im back now and to get into riding again I grabbed a 2014 ktm 250sx and tore it down to the frame and rebuilt it. For the engine I only did a top end but regardless bikes all back together now. Ive been chasing spark issues for WEEKS.

The bike before tear down was great 0 issues, now when I put a new plug in (running a BR9es) it runs great for like 30min to an hour and then dies. When I pull my plug its not fouled, perfect color and not soaking wet so its not fouling plugs. If i then take the plug and test spark on side of engine it no longer sparks or hardly sparks on the side of the plug not in the correct spot... add new plug and its back for a while. The changing plug could be a coincidence but regardless this thing kills plugs and runs great then just dies and wont run again its so weird.

I changed the Ignition coil with no change, pulled stator off and it was dirty cleaned it and new plug bikes runs great, rode for 30 min seemed good so went to track and rode an hour and it died and wont start again.

Stator ohms rating comes back in spec for manual... only thing I can think of its Stator is shot or CDI box is bad.

Again its not fouling plugs and runs beautiful until it doesn't. please help me out here Im so sick of dealing with this. thanks everyone.

[Shhhh]

You should be running a BR8 plug, not the 9.  Not sure that is the issue, but a good place to start.

Edited October 30, 2022 by Shhhh

[JJ10]

2 hours ago, Dirtbiker227 said:

 

Stator ohms rating comes back in spec for manual... only thing I can think of its Stator is shot or CDI box is bad.

I think you answered your own question.  Might be CDI, but before buying parts and hoping for the best, I would go through every inch of wiring and check connectors.  You said it ran great before you tore it down.  That should make you suspect that something wasn't right at reassembly - broken wire, loose connector, etc.  Think about what changed between the time you brought it home and now.  Probably something about the teardown/reassembly.

A hotter plug is not the answer.

[adam728]

Put in the proper plug and try again. Too cold can carbon the insulator nose and short out the plug. I've been down this road in the past. 

[Dirtbiker227]

3 hours ago, Shhhh said:

You should be running a BR8 plug, not the 9.  Not sure that is the issue, but a good place to start.

I agree i dont thi

 

3 hours ago, Shhhh said:

You should be running a BR8 plug, not the 9.  Not sure that is the issue, but a good place to start.

Yeah i agree but doubt thats it

[Dirtbiker227]

1 hour ago, JJ10 said:

I think you answered your own question.  Might be CDI, but before buying parts and hoping for the best, I would go through every inch of wiring and check connectors.  You said it ran great before you tore it down.  That should make you suspect that something wasn't right at reassembly - broken wire, loose connector, etc.  Think about what changed between the time you brought it home and now.  Probably something about the teardown/reassembly.

A hotter plug is not the answer.

I will check wires but already have and right so youd think its wire or cdi or maybe stator but idk, i heard these 2014s are known for bad stators from the factory. And the only thing that change's is unhooking wiring and stuff but these bikes are so simple unless its cdi or stator idk what it would be. Ill check wiring again tmrw but idk why wiring broken would cause it to cook plugs. It also sucks the only way for me to test it is a new plug and riding for an hour, this cutting out randomly is super dangerous.

1 hour ago, adam728 said:

Put in the proper plug and try again. Too cold can carbon the insulator nose and short out the plug. I've been down this road in the past. 

I will but before the teardown it was running a br9 with 0 issues so idk why all of a sudden it wouldn't like it…

[JJ10]

31 minutes ago, Dirtbiker227 said:

I will check wires but already have and right so youd think its wire or cdi or maybe stator but idk, i heard these 2014s are known for bad stators from the factory. And the only thing that change's is unhooking wiring and stuff but these bikes are so simple unless its cdi or stator idk what it would be. Ill check wiring again tmrw but idk why wiring broken would cause it to cook plugs. It also sucks the only way for me to test it is a new plug and riding for an hour, this cutting out randomly is super dangerous.

I will but before the teardown it was running a br9 with 0 issues so idk why all of a sudden it wouldn't like it…

Disconnecting wiring could partially break wire if there is any corrosion under the insulation, or loosen the connectors - it's a possibility worth looking at before you start replacing parts.  It's not cooking spark plugs.  The symptoms you describe sound like it's running on a weak spark (low voltage), and as soon as a plug gets a slight bit of carbon build up, there isn't enough voltage to fire through it and burn it off.  Carbon fouling - not oil fouling.  That's why I suggest that going 1 heat range higher isn't going to solve the problem.  Very little difference between a range 9 and range 8.

[Dirtbiker227]

37 minutes ago, JJ10 said:

Disconnecting wiring could partially break wire if there is any corrosion under the insulation, or loosen the connectors - it's a possibility worth looking at before you start replacing parts.  It's not cooking spark plugs.  The symptoms you describe sound like it's running on a weak spark (low voltage), and as soon as a plug gets a slight bit of carbon build up, there isn't enough voltage to fire through it and burn it off.  Carbon fouling - not oil fouling.  That's why I suggest that going 1 heat range higher isn't going to solve the problem.  Very little difference between a range 9 and range 8.

Ok i appreciate the help! Ill look super good tmrw for broken wires and make sure thats not it. Plug def could be fouling from carbon but idk when i put new plug in and check spark its a crisp blue spark and pretty strong, after bike dies it doesnt spark at all even if i clean plug. Ive even take the plug that “died” cleaned it and put in another bike and they dont spark at all anymore so seems like it kills it idk.

 

either way ill check wires tmrw as well as cdi ohms rating when the bike is warmed up and toss the br8 plug in it but ive always ran br9s so i doubt thats it. Ill keep you updated!

[JJ10]

23 minutes ago, Dirtbiker227 said:

Ok i appreciate the help! Ill look super good tmrw for broken wires and make sure thats not it. Plug def could be fouling from carbon but idk when i put new plug in and check spark its a crisp blue spark and pretty strong, after bike dies it doesnt spark at all even if i clean plug. Ive even take the plug that “died” cleaned it and put in another bike and they dont spark at all anymore so seems like it kills it idk.

 

either way ill check wires tmrw as well as cdi ohms rating when the bike is warmed up and toss the br8 plug in it but ive always ran br9s so i doubt thats it. Ill keep you updated!

Good idea to check it when it's hot.  Heat increases electrical resistance, and your electronics are sensitive to that.?

[zig06]

Try running a BR8egv Iridium plug.

[Dirtbiker227]

17 hours ago, JJ10 said:

Disconnecting wiring could partially break wire if there is any corrosion under the insulation, or loosen the connectors - it's a possibility worth looking at before you start replacing parts.  It's not cooking spark plugs.  The symptoms you describe sound like it's running on a weak spark (low voltage), and as soon as a plug gets a slight bit of carbon build up, there isn't enough voltage to fire through it and burn it off.  Carbon fouling - not oil fouling.  That's why I suggest that going 1 heat range higher isn't going to solve the problem.  Very little difference between a range 9 and range 8.

Hey after looking at the bike more today with a new plug i think your right, super low spark that gets overcome eventually. So if were saying its weak spark arent we talking bad stator?

[Dirtbiker227]

Ok so checked every wire on the bike, no breaks or issues. I think JJ10 is right the bike is technically fouling the plugs but not like a normal foul these plugs are hardly dirty because spark is so weak. That makes me think its the stator, so im going to try replacing that.

[dirtripper]

I had similar issues on an older KTM.  Turned out to be the CDI.  No way to diagnose a CDI problem, just finally got tired of chasing the problem and bit the $ bullet.  Never another problem.

[JJ10]

23 hours ago, Dirtbiker227 said:

Hey after looking at the bike more today with a new plug i think your right, super low spark that gets overcome eventually. So if were saying its weak spark arent we talking bad stator?

Not necessarily the stator - but could be.  I would suspect the CDI first, only because it's an electronic control more susceptible to fail.  The stator is just a wire winding that basically can last forever unless it gets severely overheated or loosens up and crashes against the rotor.  If it were mine, I'd check the stator to be sure no windings are shorted out, and make sure it's tight.  If the stator checks good, then replace the CDI.

Edited November 1, 2022 by JJ10

[Turn,TheScrew]

Picture of the perfect plug color, that doesn't work?

 

[Dirtbiker227]

On 11/1/2022 at 3:27 PM, JJ10 said:

Not necessarily the stator - but could be.  I would suspect the CDI first, only because it's an electronic control more susceptible to fail.  The stator is just a wire winding that basically can last forever unless it gets severely overheated or loosens up and crashes against the rotor.  If it were mine, I'd check the stator to be sure no windings are shorted out, and make sure it's tight.  If the stator checks good, then replace the CDI.

Well i already ordered the stator so we will see, to me cdi doesn't seem plausible since this bike has 80 hours on it, and 2014 ktms had issues with stators. Also bike runs so good, no hard start, no idle issues or rough running even when hot, just cant use a plug thats slightly dirty idk to me seemed like stator. Lets hope im right. I will update when it comes in so anyone who finds this thread later on can see but thanks a bunch for your help!

[JJ10]

13 hours ago, Dirtbiker227 said:

Well i already ordered the stator so we will see, to me cdi doesn't seem plausible since this bike has 80 hours on it, and 2014 ktms had issues with stators. Also bike runs so good, no hard start, no idle issues or rough running even when hot, just cant use a plug thats slightly dirty idk to me seemed like stator. Lets hope im right. I will update when it comes in so anyone who finds this thread later on can see but thanks a bunch for your help!

I'll be curious to see if the stator solves it.  When do you expect to have it?

[Dirtbiker227]

On 11/3/2022 at 12:56 PM, JJ10 said:

I'll be curious to see if the stator solves it.  When do you expect to have it?

Just came in today, chucked it on the bike and no change. Bike fired up with old plug and died after about 10 seconds never to start again unless i put a brand new plug in but it “fouls” that too. Super weak spark. I guess this means im ordering a cdi box now? Pain. in. The. A$$!

[JJ10]

7 hours ago, Dirtbiker227 said:

Just came in today, chucked it on the bike and no change. Bike fired up with old plug and died after about 10 seconds never to start again unless i put a brand new plug in but it “fouls” that too. Super weak spark. I guess this means im ordering a cdi box now? Pain. in. The. A$$!

Yeah, I would have suspected electronics over electrical.  It's why I don't get excited about fuel injection.  Fine when it works, sucks when it doesn't,  never gives you any warning before it fails, can't be serviced in the field, and can't be diagnosed but by process of elimination.  So now you've eliminated one of three components that could be bad.  It's either the CDI module or the coil.  Didn't you say you already replaced the coil?

7 hours ago, Dirtbiker227 said:

Just came in today, chucked it on the bike and no change. Bike fired up with old plug and died after about 10 seconds never to start again unless i put a brand new plug in but it “fouls” that too. Super weak spark. I guess this means im ordering a cdi box now? Pain. in. The. A$$!

Yeah, I would have suspected electronics over electrical.  It's why I don't get excited about fuel injection.  Fine when it works, sucks when it doesn't,  never gives you any warning before it fails, can't be serviced in the field, and can't be diagnosed but by process of elimination.  So now you've eliminated one of three components that could be bad.  It's either the CDI module or the coil.  Didn't you say you already replaced the coil?

[Turn,TheScrew]

I'd be disconnecting and cleaning every electrical ground. 

Unscrew bolt, clean frame and contact. Put back together. 

Edited November 8, 2022 by Turn,TheScrew