06 WR450 top end sputter

I've been racing my 06 WR450 on the ice all winter, but it has developed a serious top end sputter. It feels and sounds like a rev limiter is kicking in at ~8000rpm and it just won't rev any higher and the power seriously drops off. I haven't changed anything since last weekends ride (same tank of gas- 1 week old, then topped up with fresh today after it started misfiring) and the jetting is the same as always. It has run fine on both colder and warmer days than today. It started out really subtle, but got worse and worse every lap. I made it do it for a few seconds then did a plug chop. It looked pretty white, so I upped the main from a 165 to a 180, which made no difference. I also just checked the valves and changed the oil, and nothing is out of the ordinary.

I don't know what to check next, and thought I should ask since a search didn't help much.

This sounds like the same problem I have with my 2002 WR426 and I posted it as breaking up at WOT. My bike runs fine at low and mid range but when it goes to WOT seems like a rev limiter kicking in or similar to a 2 stroke when running lean but without the detonation. I checked the TPS, increased the main jets in steps with no change. I am getting ready to do some electrical testing and will go on from there. If you resolve the problem please post what took care of it and I will do the same.

It could be the beginning of a stator failure. It could also be a coil issue though it is usually the stator. Testing sadly it often passes. As the bike gets more and more time on it, the stator gets worse and worse and you evetually cannot ride it all. In some cases, the bike revs out fine when cold but withing a few minutes time, the issue return as it gets hotter.

I found the throtle stop screw completely removed from my carb so I made up one to test since the local shop didn't have it in stock and the problem is greatly reduced so my problem may just be that the screw needs to be put in.

Ah, you probably went over center at WOT, you are lucky it did not lock up!

It could be the beginning of a stator failure. It could also be a coil issue though it is usually the stator. Testing sadly it often passes. As the bike gets more and more time on it, the stator gets worse and worse and you evetually cannot ride it all. In some cases, the bike revs out fine when cold but withing a few minutes time, the issue return as it gets hotter.

Two years ago I took my bike to Tokyo Mods to fix what sounds like the exact same prob. Almost $500 later they returned the bike to me running the same as I dropped it off, no change. I never thought of the stator, I guess neither did they. Sold the bike since then.

I have the motor torn down at the moment and nothing is wrong with it. I fixed a CRF450 a while back that was doing the same thing and it turned out to be a big end rod bearing that was about to let go. Mine is fine, but I don't have time/cash to mess with it as I'm a full time student. At this point it has to be something electrical, and I have done all the tests in the manual.

I was going to upgrade to a Dynatek cdi this summer, but I guess I'll have to have a closer look at the stator first.

Keep in mind, the stator may well test fine according to the manual. They manifest a failure typically as a high speed miss that gets progressively worse of time and with temperature.

Two years ago I took my bike to Tokyo Mods to fix what sounds like the exact same prob. Almost $500 later they returned the bike to me running the same as I dropped it off, no change. I never thought of the stator, I guess neither did they. Sold the bike since then.

They should not of charged you if they did not fix the problem. And people think places like that are full of tech Gods. Shameful actually the crap they pull.

The stator looks almost melted at some of the edges, with corresponding marks on the inside of the flywheel. I slapped in a new stator and it runs as good as new. Any insight how this happened?

stator.jpg

could your crank bearings be starting to wear? Im just guessing,no experience .Maybe when you are starting to beat the snot out of it the crank moves closer to the stator poles.Again just cheap internet advice, No experience with the situation.

I have seen old RM125s back in the day run with what it seems like 1/8 inch play in the crank.

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