400ex Jetting

[tommydogtv]

I have a 2003 400ex. I am going to get a uni air filter. When i get it would it make sence to put a bigger jet in? If so what size will give the best performance?

[1fast400ex]

i would not rejet for just a high flow filter.

[cals400ex]

i would not rejet with just the filter either . if you were removing the airbox lid, then maybe go from the stock 148 main jet to a 150. however, in the cold winter months, it may run better with a 150 even with the lid in place. most people do change the pilot jet on the 400ex's because they are known to be hard to start. the stock pilot jet is a 38. most people go to a 40 or 42 if the bike is stock or near stock. however, the main jet is what matters for full throttle. the pilot jet is for starting the bike to 1/4 throttle or so. the needle taper and clip position is for 1/4 throttle to 3/4 throttle.