Gray wire?

Ok I sure that is has been bought up before in this forum but couldn't find anything on it. I just got my new 2004 WR450F on Friday. I have cut the throttle stop and removed the exhaust baffle. The bike runs really hard. Couldn't believe how much power it had. Well I want all I can get and is it possible to cut the gray wire without have the cam timing advanced. I can do this gray wire mod myself but will take my WR in to the dealer to have the cam timing advanced. Just wondering if I cut the gray wire without have the cam timing advanced will be ok to do??? I'd appeciate any info. Thanks...

Well there's good news and bad news. Yes you can go ahead and cut the grey wire and it will work with either cam. The bad news is you can't advance the cam timing on the 450 like you could on the 400/426. If yo do you will lose the auto decompression feature (and probably electric start as well). You will need to replace the cam with the exhaust cam for a YZ450 in order to retain the decomp. Part can be had for about $100 depending on where you get it. Retail is about $150. Not sure what kind of riding you do but for desert the YZ cam is well worth it. For tight technical trails it might be a bit of a beast.

that's new news to me. I have read and have been told that the 2004 WR450F is off one tooth on the cam, and my dealer told me to bring it in after breaking it in and they would advance it one tooth for more power. Now I'm really lost! HELP

Don't fret, it's no big deal. You can rotate the cam one tooth but like I said the decompression mechanism will no longer function. Replacing the cam really doesn't take much more effort than rotating the existing one. Both jobs require the about the same amount of dismantling. I did the whole job in a couple of hours. It just costs a little more for the parts. Personally I wouldn't give up the decomp and although I haven't tried it I would bet the electric start won't work without it either. This link is for the WR250 but the info on the cam mod pertains to the 450 as well:


I was at the Yamaha Dealer recently gettingsome parts and the have a "Service Bulletin" Manual that describes the closed course competition upgrades for the WR450. They are (of course) remove the air box cover, remove the exhaust baffle and remove the gray wire (six pin connector going to CDI unit).

The manual also states that re-indexing the WR cam to YZ cam will cause the electric start to fail and may become harder to start. Keep in mind that the auto-decompression function is inherently timed with the cam, and that changing the cam timing will also change the auto-decompression timing. Without the decompression lever, as found on earlier models, this could make starting hard or even painful. If you want easy electric starting you and you want the YZ timing, you will likely have to buy a new cam.

Eihter way you should be able to get your local Yamaha Dealer to let your look at the manual.

PS. If you go for the YZ cam and want to get ride of the WR cam, PM me and lets see what we can work out.

I have done the cam mod on 3 bikes now. two of them were the yfz four wheeler and one was a 2004 wr450f. I have had NO PROBLEMS with any of these starting even with the decompresion being ONE TOOTH OFF! Long story short. Rotate the cam for free or spend a $100 on a yz450f cam. I choose the free method personally.

thanks guys for the feedback. I think I'll just leave it alone for now. The bike still is a rocket ship just the way I have it now. So I guess it's ok if I cut the gray wire??? Still not quite sure what to do with that mod? :):D

Hi !

Sorry, After reading all material I still didn't catch what the gray wire cut will generate to the WR 450 2004.

Is this a RPM kind of control ?

What do I loose (or win) ? How safe it is ? :)

I run long rallyes in far places, so speed and reliability must go together in my case.

Thank you in advance !

Luiz Lobo

it supposed to advance your timing curve once cut. At least that's what I understand. I want to cut this wire but not quite sure if I should or not.

Don't cut the grey wire. Disconnect the connector and push the terminal for the grey wire out of one of the connector bodies.

That way you can ride it and see what you think. If you don't like it or see any performance change, you can reconnect with no problem.

If you check the site "" you should be able to find more grey wire information. Check this link for more info and a graph of the spark advance curve with and without the grey wire. grey wire info.

PS. I'm not sure how much value disconnecting the grey is with out the throttle stop mod, and maybe the YZ cam.

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