Jet or NOT?

I just purchased a K&N filter for my quad and im planned on running it with the air box off with an outwear and i have no other mods yet but i was wondering if i still should re-jet it?

[Ben]

In my opinion you would be smart to rejet your quad when adding a higher-flow filter and removing the lid. Your quad will breath much better and that will change the intake dynamics. I know some of my buddies only rejet if they add a new pipe but I think it is good policy to rejet whenever you make a major intake change (pipe, filter, lid removal).

[crowdedhead]

yes you need to rejet...adding the k&n filter and removing the lid is almost pointless if you dont.

[Doibugu2]

I have the K&N filter, and leave my airbox lid on, and I rejetted. But I actully went down from a stock 148 to a dynojet 142. I did notice a nice throttle response change from it. My Eleveation is 800ft.

How is it running not that you have your lid off? Is it bogging out anywhere along the powerband?

[AtvMxRider]

Yes you are most likely going to have to rejet. I have a K+N no air box lid and I run a 155 main. it ran a little rich until I took the airbox lid off. not it runs perfect.

[REC]

I have a 99' 400ex with a stock motor.
I cut a 2 1/2" hole in the airbox lid and have a no-toil filter.
I recently put in a #42 pilot jet, k&n stage 2 jet kit (#165 main) plus their needle with the clip in the center position.
I thought I was running a little rich, and went back to a 160 main and it started pinging. So i reinstalled the 165 and she runs great.
Hope this helps
Later

Ok now i know i have to rejet now how exactly should I do it? I mean ,what are the rules of jetting involving main jet and pilot?