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Yamaha WR426 Mod.02 misfire at 5000rpm

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I own a 2002 model yamaha wr426.

Here is some of my problems:

Have stutter problems at 5000rpm when i ride the bike.

Same problem without the tps connected.

Exhaust pipe become red when the bike is not moving, have checked the timing and exhaust valvs.

The regulator givs me the output voltage 3V at 5000rpm and it should give 13,3-14,3V.

Lighting coil resistance is 0,57 ohm at 10C`and it should be between 0,16-0,24 ohm at 20C`. (Maybe this is OK at the right temp.)

Spark plug is very black after a ride and I need to replace it after about 5-10 hours riding because it stop function.

Grey wire from CDI unit is not connected on my european model. I tryed to connect it, but the bike even get worst.

I have mesured all the electronic values as the service manual recommend and it`s all fine except the issue i mention abow.

This is my jetting setup: Main Air Jet (200) - Pilot Air Jet (75) - Pilot Screw 1,5 turns out - Pilot Jet (42) - Starter Jet (65) - Main Jet (178) - Jet needle (OBDQ R Groove No.4) I live about sea level.

I have also cleaning the carburator and jetts without notice some difference.

The bike has a Arrow muffler.

I hope there is someone in here ho could give me some good answers.

Best Regards



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Stutter is probably due to your electrical problem. You need to go though the manual step by step, starting with the stator and do the tests exactly as the book says.

Foget about the grey wire, spark plug and anything else. Glowing header is normal for a bike with no airflow.

Focus on the electrical. If something does not measure up, replace it. Test the stator and pickup coil all very carefully.

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Hi William1,

Thank`s a lot for your answer.

Yes I already have going through the service manual electrical chapter ,but all it mention i could test on the CDI magneto is the pickup coil resistance and this is within specification. Have also checked source coil 1 and 2 resistance and i find this OK.

As I mention the regulator givs me the output voltage 3V at 5000rpm and it should give 13,3-14,3V.

Could this have somthing to do with the stator or pickup coil? Or is it just a broken regulator?

Any suggestion how else I could test stator and pickup coil?

I would like to test the output voltage, but how and what is the correct voltage?

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i would say none of your problems are being cuased by your carb or jetting or your pipe. as for it glowing i would think either its just not getting airflow but it could be a timing advance more than neccecary wich would also cuase the plug to be black and the misfire. so that would show you may have a bad cdi or if your magneto plate has an adjustable timing curve then just adjust for performance. as for you only getting 3v at 5000rpm i would think you have a bad voltage regulator. cdi failure is usually due to a bad regulator. so i would try to adjust your timing, if possible you would have to take off the flywheel and you would see three to four screws with oblonged holes for adjustment. if not that then change your regulator, as long as everything else checks out to service specs, and see if you get correct voltage if you do and still arent getting the performance then i would look to your cdi.

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Have now measured the output voltage from the stator and it shows 110V AC at idling and 90V AC at 5000rpm. The question is: Is this good or bad?

Checked the regulator again and it shows 12,2V AC. When I measured it before I had the fluke on DC power :-(

By the way, the bike is also quit difficult to start, even if its hot.

Timing on the bike is fine.

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The manuel says nothing about voltage output on the stator or the pick-up coil. It is only mension the resistance and this is OK on both. I have tryed to search on the nett for more info about this, but without any good results.

Have also taking apart the CDI Magneto system just to check the condition of the pick-up coil, rotor and stator, it looks brand new. Also checked the wires from CDI magneto up to CDI unit.

Is it possible to measure output voltage from pick-up coil and if what should it be?

There are 7 wires going in to the CDI Magneto system.

Red and white goes to pick-up coil

Brown and green goes to Sourcen coil 1 (This is were i measured the 110v AC to 90v AC)

Pink and Green goes to Source coil 2

Black and yellow goes to lighting coil.

The bike has been at a yamaha workshop for 3 mounts, and they was not able to find a solution.

So I`m desperate to get this bike up and running!

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