1981 YZ125H Electrical Question

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9/4/2018 7:43 PM

After a partial restoration of my 1981 YZ125, the bike seemed to run fine for about 20 minutesof dirt riding, then started to pop a little and seemed to be loosing power on hills. After stopping and pulling the stator cover we discoverd the wiring in the stator compartment was melted and smoking. Would this possibly hurt the CDI unit, or the ignition coil? I’ve found a company that produces new stators in California, but I don’t want to smoke another stator if the problem lies elsewhere.

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9/4/2018 8:54 PM
Edited Date/Time: 9/4/2018 8:55 PM

might have fried the cdi. no easy way to tell until you try another stator and see if it runs. unlikely it fried the coil but the coil can be tested to some degree. you can also look on ebay for a used stator.

i have never seen a melted smoking stator so something very odd happened.

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9/5/2018 7:57 PM

I agree, something strange happened. I’m purchasing a new stator from a stator shop in California. I’ll be testing all the other electrical items, before I attempt to start it again.

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9/7/2018 6:28 AM

I replaced all the electronics on both my 1981 yz125 restorations only because I don’t ever trust almost 40 year old electrics. The stator is where your power begins so good possibility it could have affected the CDI and coil. Make sure you have no shorts or breaks in any of the old wiring also. Photo
Photo
Photo

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9/7/2018 6:49 AM

Thanks! I plan on inspecting and testing everything when I receive my new stator.

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9/8/2018 11:27 AM

Check out the magneto/flywheel. Definitely arcing going on. It melted the magnets. Photo

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9/8/2018 11:43 AM

Wow. Was the stator real tight to the flywheel. That thing has serious damage.

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9/8/2018 12:43 PM
Edited Date/Time: 9/9/2018 7:02 AM

Yes, the tolerance is very close. Complete meltdown.

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9/8/2018 2:15 PM

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9/9/2018 9:05 PM

New stator in place, waiting for the flywheel to arrive. Photo

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9/14/2018 7:44 PM
Edited Date/Time: 9/14/2018 7:45 PM

OK, did some thinking and reconstructing of events and have pretty much figured out why this happened. When My son and I installed the flywheel, then went to set the timing, we had to rotate the stator plate all the way, full lock, to the right to get the timing correct. All the pics I've seen, and from what I can remember, the timing was correct when the stator plate was more centrally adjusted. So, maybe the flywheel wasn't positioned over the woodruff key, so the flywheel was off. If that was the case, that would account for having to adjust the stator plate rotated all the way to the right. If this was true, the flywheel would have been slightly off center, on the shaft, causing the flywheel to bump into the stator plastic housing and may have worn through the stator plastic and touched coil wires causing a short.

No sure if you can tell in the attached picture, but if you zoom it, you can see the woodruff key slot to the center, left, and silver metal just to the right of that, where the woodruff key actually was positioned when we torqued the flywheel bolt down. I think that is why we experienced the failure.

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9/14/2018 7:46 PM

Here’s Photo the flywheel pic.

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