YZF250 Stator?

Hi, I have a 2008 YZF250 that runs well at idle and moderate RPM. The problem occurs at higher RPM; the bike will sputter and backfire slightly. The carb and jets have been cleaned thouroughly and now I'm being told it's the stator that's causing the issue. In my mind, a stator is nothing but wound wire that unless hit with a sledgehammer couldn't possibly break. Is there other components associated with the stator that could cause limited ignition at high RPM? Thanks.

Have you cleaned or replaced the spark plug?

Or checked your spark?

Or checked your spark?

Yes, the spark plug is good and it looks like there's good spark. My question is mainly if there's associated other elements that come with the stator? And would a stator even caue this problem in the first place since it runs well at idle?

The stator is actually made of two parts, the colis, which are varnish covered copper wire on an iron core and a crank position sensor that tells the CDI when to fire.

Stators go bad all the time, the varnish fails, the coils short out and power output drops off. As they heat up, often the situation becomes worse. If output is marginal and the engine is running at high rpm, the electrical demands are high. If the stator fails to keep up, misfires occur. At idle, the output of a marginal stator is typically more than able to kee it running without a hiccup.

The crank position sensor is a similar device, only the wires in it are much smaller. It too, fails in similar fashion.

Keep in mind, ignition coils also fail in similar fashion. When tested at room temperature, they can often test as satisfactory.

Electrical parts do not like living in a a nasty environment like an engine.

Thanks! That's a very reasonable explanation. The only thing that I might have a slightly different perspective on is that I'm not sure if I've heard of very many "stators" going bad with respect to the true sense of the word stator. (the wire wound iron core part of the stator). Not much can go wrong with that and I would assume that the varnish is of sufficient durability to withstand a fair bit of usage. The crank position sensor is a good bet although it comes as one part as you have said. Thanks again.

Actually, alot can go wrong with a stator. There are companies who specialize in stators because of the demand (ie, Ricky Stator)

To a certain extent, the oil weakens the varnish, as does the heat. The vibrations are not pleasant either. Of all the electrical parts on a bike, after the battery (if there is one) the stator is the next most common electic part failure. Next would be kill switches, then main harness, then coils, then CDI's. Biggest cause of non-part electric problems is bad grounds followed by poor connections.

Good information to have. Thank you. And here I thought all that stators were asked to do was follow the law of physics and no more. I'll take back all those nasty thoughts I was having of the dealer. For now. haha

Stators like we have on most small bikes is very old technology, dating back to the 40's. Big modern road bikes have modern alternators. We are just barely removed from rubbing a cat on a wool blamket for electricity.

Stators like we have on most small bikes is very old technology, dating back to the 40's. Big modern road bikes have modern alternators. We are just barely removed from rubbing a cat on a wool blamket for electricity.

Ha ha!! I'm picturing a cat zip-tied to my back tire and a wool blanket on my fender with some wires as my emergency back up system

Hey, do not laugh, it works..... :smirk:

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