Just bought a WR426, took it out for a ride to run it in, noticed it was missing at about quarter throttle. Thought it was the jetting but I can't jet it out of it. Swapped the TPS and CDI over with another one but it still did the same. We are pretty sure it's in the electrical/computer system somewhere but stuffed if I know what it is. Has anyone else encountered this problem? Have got a 99 WR400 and have had no problems with that.

are you looking for us to agree with you or give you some pointers?

IMO get a PAJ Screw & turn it out to the equivelant of No 125. it'll cost you $12.

of course i also recommend you completely change the wiring harness & the carb. the earth to the frame can be dodgy so of course you'll need a new frame.

sorry to bring the bad news...


I guess I don't get Brit humor. I think I'll try a warm beer, and read it again.


Pretend it's flat and give it the gas.

Talk to your dealer again. It might be something simple. Missing is can be caused by a variety of things, but you mentioned it was 1/4 throttle.. Only 1/4 throttle? If it is a Mapping problem The Yamaha Uses a Throttle position sensor, a CDI control computer (electronic system used to advance and retard the timing) and a Neutral Switch which retards timing at Idle to reduce emmissions.

If you have tried jetting and Air screw adjustments and its still 1/4 throttle the possiblity may be either a leaky accelerator pump (you didnt mention if it was a continuous miss).. a shorting Spark plug that is "popping" in and out at a certain voltage.. (as you said.. 1/4 throttle).. Or could be bad grounds, but I kinda doubt it in all honesty.

Was the Carb spotless? did you remove all Jets and inspect for a pilot jet or air jet plugged off?

I wish I could be more specific in helping you, but I need more info.

If you have tried anything else, leave a post and ill see if I can offer more Ideas.

Good luck..and if shes Still under the 30 day warranty.. PLEASE take it in!.. :)

Take it back to the dealer before the 30 warranty is up. Don't mess with it. Let them recreate the problem and fix it.

I've had the same type of thing go wrong on my bike. I tend to think it's the stator. Unfortunately, I chased the jetting ghost for far too long believing that I was on the right track and now will be paying for the repairs myself.

If you have another bike, be satisfied for a little longer.

I feel your frustration ! Good luck.


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