What's a BK Mod and Grey wire Mod ? ? ?

I wanna know what is exactly a BK Mod and Grey wire mod.......? May I make this mods in my '99 YZ400F....? I'm reading so much about these mods here but I got no idea what are all about ?

Thanks for your answers ! :)

You cannot do the Grey wire mod. That is for WR models.

You cannot do BK mod, that is for 2000-up models. However, you can do something similar to the BK mod for your bike. See this thread BK mod for 1998/1999 started by NH Kevin. Basically, your carb accelerator pump generally throws too much gas in when you wick on the throttle - there is a 2 or 3 second stream thrown. You can limit this to about 0.5 seconds by shortening the throw of the accelerator pump. On the 2000-up bike there is an "ear" or tab on the side of the carb that you can drill and tap to palce a set screw to shorten the throw. On the 98/99 there is no tab but the thread above give ideas on how to shorten this throw...

Picture of the BK mod are on motoman393's web site which will give an idea of what is happeningclick here


Steve T


I don't have a WR so I can't give you good information. But if you go over to the WR side of Thumpertalk and click on the word "search" in the upper right of the screen, you can enter "grey wire" to get more info.

Basically it's a grey wire that runs underneath your gas tank. I think it has something to do with retarding the ignition or timing. If you cut it, you will have immediate performance gains.

I am not sure if non-US bikes have this wire...


Steve T

I own a 2001 wr426 what is the grey wire mod and how do i do it

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