Grey wire

I just joined up with ThumperTalk after reading posts for a couple of weeks. Purchased my first Thumper 1-1/2 months ago, a '02 WR426. Been a 2-stroker all my life (at least off-road) and decided to convert. Lovin' th WR and must say I am still learning the 4-stroke technique but now, after about 325 woods miles, it's coming together quite wonderfully. Oh, and the hill climbing attitude it has!! :) Will never return to the 2-stroke, except for "Novelty" only.

Anyway, question is: What are the wires you guys are disconnecting? I assume that one is a rev-limiter, what is the other? I uncorked the bike, the airbox, exhaust and throttle stop, and am happy with the R's I get now, but it does seem to hit some sort of limiter at high RPM. Is it really safe to rev much higher?

Any help is greatly appreciated. I already love the site/forum and hope I have some usefull input for you guys as well!

Oh, and by the way, I do recall reading on Yamaha web site that the WR450 is about 6 lbs lighter that the '02. The link was removed a while back.

I am not POSITIVE, but I belive that the disconnection of the grey wire allows the bike to run off of a different CDI mapping, one that is smoother and allows the bike to run much better.

I have done this, and I found that my bike lost the stumble that I would get when I was bombing down the highway, seemed like the bike rolled on the power smoother, and it did not detriment the economy.

As for the wire, take off your tank, and look for a 2-wire black connector that has a black/w white wire and a grey wire. Disconnect that black connector, and pull the grey wire out from the back of the connector (I then pushed the grey wire up into the insulation) then reconnect the black connector.

That is all that is required.


Some cut the wire, but if you get the wrong one, well, then you get to work on your wire reconnection skills.


Thanks, I'll try it before this weekend's ride. I've seen some talk about another wire, lt. blue I think?

Search for "Grey Wire" mods and you will find all of the information you will need including clear pictures. Seemed to help my bike. If you only disconnect the grey wire, you will still have a rev limiter. Don't attempt to disable your rev limiter or you will probably be sorry. I can easily rev right into mine without trying too hard. Without it you will probably overrev sooner or later.

Light blue wire, part of the six pack coming out of the CDI. This is a neutral line, that lowers the CDI output when in neutral. Some have reported better starting once disconnected, supposedly do to a better spark in neutral. I cut mine, and didn't notice any difference..........but my bikes alwasy started easily.

Dodger :):D

Man for being least effective mod it sure gets the most attention. The grey wire is on the US WR bikes for emissions. It prevents the engine from emitting too much noise, thus being able to pass the feds sound test.

From what I’ve read, it helps the 250’s more than the 4xx’s. On my 02 I noticed a little better engine mid throttle control and that was all. Depending on how you’ve modified your bike you may feel more of a performance gain IMO.

It’s a very simple mod and won’t harm the engine in any way. Go for it!


Highsider1, try the YZ timing and EMM needle… You’ll love it!

I'm going to add a switch in-line so I can toggle back and forth between gray line and no gray line... Should give a good indication of whether or not it does anything.

While you’re at, you might want to do the blue wire mod. It cuts down the spark intensity while you’re in neutral.

Do this mod if you are fouling plugs.



(((Thanks Motoman393 for the tech pics!)))

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