Jetting w/yoshimura system

[HondaRider250]

Has anyone jetted a 400ex with a yoshimura system and k&n air filter? what are the jetting specs? also, (not to ask a stupid question) where is the main jet located? im helpin my buddy out whos got a 400ex

[buster024]

I just did mine a few weeks ago. I don't know what jet kit you've got....I used Dynojet. I bought the RS-3 full exhaust, and I've got a k&n. The main jet is on the bottom side of the carb. You've got to basically get to it with a socket by hand. I can't remember the socket size (anyone??). Make sure to turn the gas switch off, and bleed the gas in the carb, or it will pour out. You'll feel the jet underneath the carb (it's probably poking out a port at a funny angle). Put the socket on it and turn gently. I turned to hard and sheared the brass jet off inside the carb and had to take the whole carb out. If you do that, don't worry, it's not that hard, just a pain in the butt. I used the recommended 170 jet, then follow the instructions about the fuel mixture screw.
Mine didn't run right with the airbox lid off, so I threw it back on. I'm still not quite satisfied with it, so I may try a different needle combo, or fuel mixture screw combo.
Good luck!

[buster024]

I'm assuming your jet kit with come with instructions, but if it didn't for some reason, you've also got to change the needle and needle setting. If you need help with that just ask.