wr426f 2002 doesn't run well

Hi! i have a problem with my wr426. here's a vid




the biggest question for me is that sometimes it starts well and work properly, but after 5-10 min ride it works like this. and sometimes it works bad from the beginning (when the engine is not hot)


what i tried to solve this:

changed carb

changed Plug cap assy

changed CDI

checked and adjusted valves

checked piston, cylinder and


nothing helped...


does anybody have any ideas?..





The glowing red header is normal for these bikes.  They typically do it at idle with no airflow.  So as long as the bike is running OK, don't worry about the glowing header.  I have a 250 and a 450 and they both do it.  

Thanks for  reply!

but the problem is not in the red header. you can hear how it works weak. 


on this video i give less gas but it sounds much better (just as it supposed to, acually)




tha problem is that it does-nt give anough power and just doesn't go fast...

That sounds like a completely stock bike with the original silencer tip still in place.  If so, you need to look up the free mods.  They will make a huge difference.  

Are you holding it wide open, or just partial throttle

it's wide open.


I'd do a leak down test on the head.

If it hasn't ever been redone, it's probably time.

Check the compression. That's usually the biggest part of power loss and is usually fixable by shimming the valves, or a valve job...

If compression checks out fine I'd look into the carb. Your header is glowing too much too easily. Mine used to glow that hot back before I re-jetted the carb. It was running so lean it wouldn't idle right, so I had the air/fuel screw turned way in to compensate so that it would idle. But when I would twist the throttle it would then run rich causing my header to glow like this. (Not burning all of the fuel in the cylinder) so basically there is excess fuel burning in your header... Once I fixed the jetting the bike idles and runs right now, but the pipe only glows after I'm actually riding it harder. At idle it doesn't glow...

If both of these check out fine and your air filter isn't clogged I would go into the electrical systems. It could be not enough spark, or a faulty sensor.

Thanks to everybody!


the problem was in faulty sensor btw (maybe it will be helpful to anybody)

i've just unplugged it and now it works great!

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