what jet should I use?

[lillbro11]

03 honda 400ex with curtis sparks exhaust, rev box, and k&n filter. I need help on this.

[speedfreek]

I'd say a 150 main and a 42 pilot

[storms400ex]

if its a slip-on 150 main, 42 pilot and 2 1/2 turns out on fuel screw

[john7x]

Go up around 10 from the stock. See how it runs. Then go up or down depending on how it is. You have to try a few to get it right.