Does the 400ex come with a 148 main? I have heard a lot of guys running 150 mains on their stock bikes. When I take it back to get it serviced I think I will put in a 150. And when you first start it up, I have to gassing it or it will die. That is probably the idle screw though.

 

yes, you can run a 150 main when stock. however, a 150 may be a little big for all stock. my stock bike ran good without an air box lid and a factory gutted pipe with no spark arrestor and a 152 main jet. these bikes are always hard to start. i would just put in a 40 or 42 pilot jet. also, if you get on your bike and its hesitating when its cold, just move the clip down one notch on the needle to richen it up. also, do all of the jetting yourself, its rather simple once you do it for the first time.