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Hello world, I got problems

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Hello, how's it going. I have a very strange issue that I hope the general brain trust here on thumper talk can help me out with. Last year I built a shifter kart out of a 2003 ktm 125sx. The bike was in a bit of an accident and the frame was bent. This allowed me to get a running engine at a fraction of the price. Its a crazy amount of fun, when it works, which is has been doing less of recently. To date I am going through stators at a rate of 1 every five minutes, its super bad. The bike is fine at idle however when I really crack it open its super fun for a minute or so and then it dies. I'm not sure if this an issue of too much draw on the stator from an accidental ground somewhere, or some other weird issue. Thanks so much in advance for your help, I really want to get back to tearing up the streets XD.

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A loose crank shaft can do a number on a stator due to vibration. I hope you’re exaggerating about a stator every 5 mins because they usually sell for $200-300 per.

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you can't kill a stator coil even by shorting out its output which is exactly what a kill switch does. so I just doubt what you are saying.

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ok, so vibration is an interesting idea, however the stator looks very smooth in its rotation even at high rpm. 

 

16 hours ago, jaguar57 said:

you can't kill a stator coil even by shorting out its output which is exactly what a kill switch does. so I just doubt what you are saying.

I cant think of any other reason than a ground fault causing the stator to build up too much current. 

 

18 hours ago, Dklassen said:

A loose crank shaft can do a number on a stator due to vibration. I hope you’re exaggerating about a stator every 5 mins because they usually sell for $200-300 per.

and yes, it actually is after just about five minutes, which is why i need to figure this out before buying another stator!!!

16 hours ago, jaguar57 said:

you can't kill a stator coil even by shorting out its output which is exactly what a kill switch does. so I just doubt what you are saying.

so would running the output of a stator directly to ground not be an issue?

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only possibility I can think of is a CDI faulty enough to draw too much current from the stator but not faulty enough to stop working

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2 hours ago, jaguar57 said:

only possibility I can think of is a CDI faulty enough to draw too much current from the stator but not faulty enough to stop working

is that possible, I thought that with CDI units it was fairly black and white, either they work, or they dont XD.

 

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as an electronics technician I can tell you that from many "miraculous" things that I have seen (problems that defy physics or that are one in a billion) we learn to never say something is impossible.

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10 hours ago, jaguar57 said:

as an electronics technician I can tell you that from many "miraculous" things that I have seen (problems that defy physics or that are one in a billion) we learn to never say something is impossible.

ok cool, thanks so much for the input. Please help educate me! Let me give you two examples, first, if a bike were running at say 9k rpm and you disconnected the coil from the spark plug would this in any way effect the stator? Second, if you were to have a bike running at again 9k rpm and ground the stator what would happen?

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pulling the cap off the plug while it is running lets the voltage go excessively high because now it isn't limited by the current draw by the spark plug. That excessive voltage can completely kill the coil or cause mini shorts in it that lessens its output power.

shorting the output of the stator coil is what the kill switch does and it is OK as long as the engine quickly dies. It does cause a maximum amount of current thru the stator coil but it is kept from being really high by the coils own internal  resistance. If you let off the kill switch before the engine completely dies then the engine probably will start running again and you'd have to press the kill button again. Repeating this process a few times could over heat the stator coil.

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Interesting, do you believe these are more likely things to happen than a CDI seeming to work correctly until suddenly messing up the stator? What should I look for in my electrical system?

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If it runs then there's no way for you to check for the mystery problem. Just replace the suspect items.

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sorry for not getting back to you guys for a while, got super busy. I've had some time to think about the issue and this is what i've come up with. The stator failed within a few minutes of riding, not at the first rev. This leads me to believe that it is something that needs to build up. This to me seems to point to something other than voltage, mainly because it seems that if there was a ground fault causing large load it would kill the stator pretty fast. On the other had if there was some missed connection between the stator and the spark plug causing voltage spikes i once again think it would kill it on first high rev. Taking all these things into consideration I believe that the most likely issue is that the bike is overheating, causing the coating on the wires to brake down leading to short circuit. Does this make sense, or are there other things I should look at first?

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no way the bottom case can overheat in a few minutes.

electrical problems can be a gradual death. trust me

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On 10/28/2018 at 8:24 PM, jaguar57 said:

no way the bottom case can overheat in a few minutes.

electrical problems can be a gradual death. trust me

I guess that does make sense, I just really wish it were a simple overheating issue. I guess I'll go hunting for grounds faults. 😤

Thanks so much for all your help everyone!!!!

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The wiring on a KTM 2T is fairly simplistic (like 8 wires or so), I'd be checking pin to pin, and pin to ground for every wire in the wiring harness at the ECM/CDI.  Make sure only the ground wires are seeing ground, and that none of the power wires are sending their signal to another wire or system.

When people said to check the stator for looseness, you can't just pull the side cover on the motor and take a peak.. You need to physically remove the flywheel (rotor) to inspect the stator assembly behind it.

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This is the third stator I've replaced. Looking at it, the ignition coil is cooked. However the lighting coils are fine which rules out heat. I'm kinda at a loss for what is causing this. I'm going to re do all the wiring and see if it gets better. Otherwise I will get it started with a new stator and measure the amps while it is running. Anything else I should look for?

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Have you pulled the flywheel to check that the woodruff key has not sheared?   I recently had a perfect running bike that stalled, after that stall it had all sorts of weird issues, sometimes it would start but run bad, etc.  I checked everything in the service manual everything checked out OK.  Finally started buying new parts (stator, coil, plug, plug wire, etc.) only to realize the woodruff key sheared and the timing was off and getting worse...just worth a check...Also, I now have good working electrical parts that I replaced for no reason, that I may part with.  

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Yeah, that was one of the things I checked early on. After really hoping stuff apart I've found some interesting stuff. First the wires from the stayor to the cdi are not copper, I checked their resistance and it is under 1ohm so probably not an issue. The second thing is that there is continuity between the spark plugs cap and the engine, ie ground. This is more interesting. On this kart the coil is mounted to the frame so I'm wondering if that is not how it's supposed be, please let me know if this could be my issue 👍👍

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On 11/5/2018 at 4:35 AM, Ss65supernova said:

Have you pulled the flywheel to check that the woodruff key has not sheared?   I recently had a perfect running bike that stalled, after that stall it had all sorts of weird issues, sometimes it would start but run bad, etc.  I checked everything in the service manual everything checked out OK.  Finally started buying new parts (stator, coil, plug, plug wire, etc.) only to realize the woodruff key sheared and the timing was off and getting worse...just worth a check...Also, I now have good working electrical parts that I replaced for no reason, that I may part with.  

do you think what i mentioned in my previous post could be causing the problem?

On 10/18/2018 at 7:04 AM, jaguar57 said:

pulling the cap off the plug while it is running lets the voltage go excessively high because now it isn't limited by the current draw by the spark plug. That excessive voltage can completely kill the coil or cause mini shorts in it that lessens its output power.

shorting the output of the stator coil is what the kill switch does and it is OK as long as the engine quickly dies. It does cause a maximum amount of current thru the stator coil but it is kept from being really high by the coils own internal  resistance. If you let off the kill switch before the engine completely dies then the engine probably will start running again and you'd have to press the kill button again. Repeating this process a few times could over heat the stator coil.

so would continuity between the spark plug cap and ground indicate an accidental ground in the system leading to too much current in the stator?

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I will have to check my KTM manual as far as if the plug has continuity to engine, but I don’t think there should be continuity as in grounded out, yet there should be resistance. If I remember correctly (I’ll confirm with manual later) there’s a value from plug boot to ground. Also on the bike the coil is grounded too by mounting bolts.

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