400ex Tuning

[ANDY'S 400EX]

Hey guys, newbie here. I got an 01 400ex with White Brothers pro meg full exhaust, k&n filter, white brothers cdi box and a k&n jet kit . My problem is under full throttle with the air box lid on it is surging and cutting out at the upper rpm's. I installed the largest jet in the kit and it runs great with the lid off but we do a lot of riding in water so I need the lid. Any suggestions on jet size would be appreciated, if that seems to be the problem.

[Colby@C&DRacing]

Your jetting is correct with the lid off, but with the lid on you are restricting the air flow alot which is causing your jetting to be too rich. It is hard to jet properly when you need to run with and without the lid

[cals400ex]

you do need to rejet each time you put on or remove the lid. jet it one way and run it like that. i would try like a 155 DJ with the lid on for starters.

just get a EHS lid and thta way you can run with the lid, with the benfits of runnign without a lid.. or you can make your own with a outerwears, and a metal ring to go around the outer edge of lid... cut a hole in it, stretch the outerwears around it, bolt the ring to it to hold the outerwears.. itll run like it does without a lid, but will keep water outta the box..

Jesse