Jet sizes

[Redride11]

Hey I was wondering all the specs on sizes for a stock 400ex motor with stock pipe (screen removed but tip still on) and Uni air filter w/ no air box lid. It would be MUCh appreciated! Like to get this together ASAP THANX!

[Redride11]

I should clear this up, i was wondering the jet sizes that i need now for having a UNI air filter no lid and the baffle taken out of the stock pipe, What size jets do i need now? ANy help would be great!

[cals400ex]

i ran a 152 in the cold winter months and a 150 in the summer. it seemed to work just fine for me.

[Redride11]

And u have the same set up as i do here? a 152 main jet thats it? didnt change anything else?

[cals400ex]

i had a similar setup. i had the welds grinded out of the header. i had a stock modded exhaust with no endcap. i also ran a uni filter and a modded airbox lid. for the cold winter months i ran a keihin 152. in the summer i ran a keihin 150. you might just try them both along with a 155 and see how they work. i wouldn't go bigger than a 155 though for sure. in the cold winter i like to move my clip on the needle down one position and in the summer i ran it in the factory position. i also ran a 42 pilot jet. i would tinker with the fuel skrew on the bottom of the carb quite a bit. i think i was probally around 1.5 to two full turns out most of the time. good luck

[Redride11]

Hey thanx SOOO much man, I'm gunna go by those jets and put them in and tell u how it goes!! thanx alot!

[cals400ex]

no problem, let us know how it goes.

[Redride11]

HEy guyz!
Just got the 400 rejetted! After a ili trial an air I ended up running a 158 main jet! and one clip down on the needle and i am also running the stock pilot jet WOW! i cant believe the power gain, its amazing jst having no airbox lid, uni air filter and no baffle will do! its AWESOME!! thanx alot for the help guyz!!

[cals400ex]

158 seems big. i would race a friends 400ex with the 158 and with a 152 and see if one makes a difference on top speed. i have a feeling that the 158 might give less top speed, but that is just from trial and error that i have done.

[Redride11]

Hmm.. Really.... well i'll see about that! thanx for the advice, i might jst terr it apart again and drop in a 152 and see wat happens. . . . I am gettin pretty good at terrin it aprt and gettin in back! ill let u kno!:D

[phebus]

Like Cal said, try it and I bet you'll like it. If you don't, just go back to what you had. My bet is you gain on top end.

[cals400ex]

yeah, there is a good chance it might not be noticable when riding by yourself. but if you get another stock 400ex right next too you at about top speed you may notice a difference. usually if your a little rich, your loose a little speed up top.

by the way, you don't need to rip the bike apart to just change the mainjet. on the bottom of the carb is a 17mm nut. unskrew that and the main is right in there. just turn the fuel off first otherwise it will pour out. some will still come out but just whats sitting in the carb. the mainjets will come out of there with a 6mm socket. good luck