Hi,
My 2002 WR426 jetting is completely stock and the only mods I've made to the bike are removing the airbox lid, cutting the gray wire and trimming the throttle stop.  I typically ride the bike at Ocotillo Wells but will probably also try the track at Lake Elsinore soon.  Are there any jetting changes I can make for the bike to be more responsive. I'm not interested in YZ timing because I don't want to give up the bike's smooth low end power but I'm interested in making the mid range more responsive and getting the bike to pull better in fourth gear.  Would installing a stock YZ needle jet and main jet make a big difference without causing any adverse side effects???  

Dolphin, I feel that im the only one here that would advise you to leave the bike alone as far as jetting goes. Im not sure that a 2002 could benefit from the "BK" mod but thats one mod that I would do if it applies to your bike (carb). If you tinker with your jetting and don't like the results you can always change it back.  

Dolphin, my ride is an 01 WR 426, air box lid removed, YZ throttle stop, FMF exhaust, and grey wire mod, I have played with my jetting to some extent and have found the stock jetting to work the best so far. I ride Ocotillo Wells and the foot hills and tracks around So Cal with out any changes and or problems, The mountains is the only time I make any jetting change and it's only the pilot, main, and air/fuel screw. Keep it simple and enjoy the ride.

not sure where you guys getting your jetting but here is what i have come up with
full white brothers e series with open endcap, yz timing, air box lid gone. since my 00wr400 is a canadian model, there is no throddle stop or grey wire. i run a 180 main and 52 pilot. plus i have the "p" need 3 down. this is what the guys at moto world told me to run. at sea level the thing is a rocket. i ride at ocotio no prob.in the mountains it is to rich. but with a 175 in it it runs great there.

ps sorry about my typing, just broke my wrist last weekend at lake marina on a ride


parx

More mid-range? Go YZ timeing. Then you will have to rejet..

SoCal