white bros R4

[Dardy]

Help please! I ordered a white brothers R4 slip on and I would like to know the proper jet & pilot to run so I can do it right the first time. Its a 2002 400ex and the only mods are K&N jet kit stage 1,I have the 6 airbox vents, and I grinded the welds on the header. Land elevation is below 3000 feet any help would be appreciated Thanks

[Steven]

I'de say start with the 165 main and work leaner. The K&N jet kit will instruct you how to set the needle and idle screw for your altitude.

Steve

[Dardy]

ok I installed the R4 and the 165 main jet. It pulls good through the gears but the last 1/4 of the throttle it will bog in all gears could someone please lead me in the right direction as how to fix this? Thanks

[OCCRA288]

You might try a 160 main. The main is all that controls 3/4 to WOT. By leaning this part of the fuel circuit out, you will be dumping less gas in the cylinder which will cause it to run slightly better above 3/4 throttle. Check your plug after doing this.

[Steve-o 400EX]

Originally posted by Dardy
ok I installed the R4 and the 165 main jet. It pulls good through the gears but the last 1/4 of the throttle it will bog in all gears could someone please lead me in the right direction as how to fix this? Thanks

Lean it out, I had the same problem with my e-series when i got.
it. I started with a 160 main jet and was way too rich and it was bogin. Take it down to a 155 or 158. Trust me it will make a big difference. I went to a 152 and am still a little rich, i should be runnin a 150. Try a 155 first and chekc the plug, o yeah and put a new plug in it because the one you got is prolly full of carbon. Then check it after a ride and see if it is rich or lean and go from there.

good luck.:macho

[Dardy]

Ok thanks for the info. I will jet a little lower. My k&n instructions that came with the kit said go for the 170 but that was with the airbox lid removed since I am only running airbox vents I shot for the 165. I will drop to the 155.

If there is alot of carbon on the plug does that mean its running too rich? Thanks

[Steve-o 400EX]

Originally posted by Dardy
Ok thanks for the info. I will jet a little lower. My k&n instructions that came with the kit said go for the 170 but that was with the airbox lid removed since I am only running airbox vents I shot for the 165. I will drop to the 155.

If there is alot of carbon on the plug does that mean its running too rich? Thanks

Yea, usually when there is a lot of carbon on the plug you are runnin to rich, the carbon is left by the fuel that is not burned.

[Steven]

make gradual changes to the lean side... don't go from a 165 to a 155. if you blubed a little at WOT with the 165 then the 160 is likely right on.

[ajr400ex]

I have a R4 slip on and run the stock jetting. My air box is stock and I run a Uni filter. With air box mods I would think 1 or 2 jets up from stock should be about right. You may have to adjust the fuel/air mixture a tad and maybe go up one size in the pilot jet.