99 WR 400 Mods

I picked up a super clean WR 400f a couple of weeks ago for $2500.00, I meen super clean. The guy who had i before me swore that he only put a little over 300 miles on it total. I kinda believe him because it had the stock tires on it, and it looked cleaner than my friends 05. It already has a White Bros exhaust, a header, and its jetted, other than that it is bone stock.

I did a couple of free mods including taking out the air box cover, and grinding down the throttle stop. I want to know more about the little grey wire that everyone keeps talking about. I found the infamous wire under the seat, well I think it the right wire. My question is what do I do whith that little wire, and in return what will it do to my bike, I want the good and the bad.

Also it it really worth playing with the cams to set it to YZ timing? Any other tips I need to know about? What should I be aware of other than having to change the oil every other ride?

Thanks all input will be greatly appreciated.


Thanks for the link, I actually knew about that one, but again there is no real mention about the grey wire. Thats the one I really would like to know about. I have heard its as easy as grounding it to the frame. Is that true?


I have heard its as easy as grounding it to the frame. Is that true?


You do not need to ground it to the frame. I've heard some guys just cut the wire.....I personally pulled the plug out of the socket( and taped it) where it goes into the CDI unit.

A couple of other mods I did .....de-octopus the carbuerator (eliminating all the plumbing that they did on the choke side of the carb).

YZ timing on the exhaust cam.

I also modified the accelerator pump (using the wheel collar mod).

James Now mod which is basically a homemade Power Now mod on the intake horn of the carb.

These are the cheap and easy mods to do to the motor. This coupled with countless others related to the suspension and handling.

Good luck with your new toy....sounds like you got a great deal!

What exactly will pulling the wire do to the performance? How does it effect the bike? What do I have to do to counter that so that my bike doesnt get blowed up. I am going to get some good long rides out in the wide open before I think of touching the cam. Im sure after the next ride I will want to do it right away though. Tomorrow I plan on riding at Dove Springs, I want to get up into the elevation to see how well the bike does. I know I may have give the screw on the carb a turn and a half when I get up there. Any suggestions on what I should run at 8000 feet?

My understanding is that cutting the grey wire causes the ignition mapping to revert to it's default setting, YZ ignition timing.

Furthermore, if you are going to do this mod I would think you want to go ahead and advance the exhaust cam one tooth as explained on other threads(http://motoman393.thumpertalk.com/tech/yztime.html ). This should get the bike to rev up through the low to mid rmps faster and cleaner.

I suprised nobody else has responded to this. There are a great many experts in this forum who know alot more than I, but that is the way I understand it. I also have 99 WR400 and have not done the mod yet. I do a lot of trail riding and the response and gearing seem to work very well for me, but I can't leave good enough alone and will likely do them in the near future.

Good Luck.

I like the WR cam timing for really tight trails, but for everything else, the YZ timing is the way to go. I would port the cylinder head if I were you, It adds a bit of power everywhere. handguards are a must, as you probably already know. I reccomend using a TeraFlex for your rear tire once your current tire wears out. When you bend your bars, I would reccomend protapers. If you want to find some other modifications to do, look at my bike in the ThumperTalk garage. Good luck with your "new" bike!

I am not going to be touching the inside of the beast for at least one season. The motor runs as strong as it did 6 years ago. So in terms of the grey wire, I should only unplug that bad boy after I have changed the timing on the bike by moving the intake cam?

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