400ex jetting

[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

[Mobile Dyno]

It sounds to me you are way rich when you put the lid on. Put the clip in the third slot from top on the needle. If it is already there than put it in the second slot. try a 155 or 160 main. I would say drop 5 jet sizes from whatever jet size you have in now and put the lid on and try it. That should get you close.

[ANDY'S 400EX]

thanks mobile dyno.

[ocitman]

i have a 155 main jet.
whats the stock size?

[Mobile Dyno]

148

[ocitman]

Thanks. i need a stock jet for higher elevations, like Sand Mountain.