What jets?

[400ex_BG_Rider]

I have a Honda TRX400EX ... and modded it with white brothers exhaust and k&n air filter. What size jets and needle should I use?

[rescue6]

We will need a little more information like

What is you Altitude?
Temperature?
Airbox lid on or off?
Full system exhaust of slip-on?

But if you just want a rough estimate on jetting I would have to say get a 155 Main Jet, Needle on 3rd clip possition, 42 Pilot jet and fuel screw 2 and 1/2 turns out from lightly seated

[Honda#4]

The things that rescue6 said is what I need to help you jet properly, so untill then I can't help you.

[400ex_BG_Rider]

It's a full exhaust system! I forgot to mention it's a 2001 year model trx. Airbox is stock with the lid on! Altitude is 2000 feet above sea level but I ride on the nearby mountains that reach 6000 feet. Average temp is around 15-20 degrees centigrade.

[rescue6]

So at 5000 foot elevation or above the manual calls for a 142 main for a stock bike. For your situation riding a roughly 2000-5000 with lid on and at roughly 60 deg f. I would suggest that you put the pilot jet back to stock if it is not already it should be a 38 you may be able to get away using a 40 pilot but it may be two rich 2 and 1/4 to 2 and 1/2 turns on the A/F screw(pilot screw) needle on the 2nd or 3rd from top and try a 145, 148 or 150 main jet that should get you close. I am jetted simmilar you can see it in my signature and my plug looks good but I do not run the airbox lid.

[Honda#4]

what Rescue said is pretty much right.