What are the stock jet sizes (pilot and main) on the 99 400ex? If everything is stock except WB Rev box, what are your opinions on upping each one of these jets one size?

Stock main is 148 and stock pilot is 38. I wouldn't change the jets if nothing has been done to the pipe or airbox. It shouldn't benefit you any.

I've heard that some people actually have 152 mains from the factory. Must depend on the state and elevation they were sold. Unless you change the airfilter or exhaust I wouldn't mess with it.

Does adding a K&N filter justify re-jetting?

Actually, I would suggest everyone evaluate their stock jetting. Even in the owner's manual it states that the jetting is lean to appease the EPA. Lean jetting isn't good for power or engine life.

Have any of you guys changed the stock jets like 86atc250r said. How would you know if you were running lean? Can someone explain.

Mine came rich from the factory, but I didn't change it until I put the MODS on it. After warming it up ride it wide open in fourth or fifth gear for 5 or 10 minutes and shut it down as soon as you let off the throttle. Pull the plug out and look at it if it's white on top it's too lean. If it's black on top of the plug, it's too rich. If it's cardboard tan it's juuuust right.

i would acually rejet the both main and poliot. main cause honda jetted lean and poliot for easier starting. rejet main to 150 or 152 and piliot to 40 or 42

Where you can find someone or company that sells pilot jets? I know a few componies that sell the main jets but no luck with pilot jets. If you know who has them and they have a website, e-mail address, or mailing address. Please post it.
Thanks

just go to your local dealer. if there isn't one close to you a piliot jet isn't nessesary just help cold starting