I'm getting the pro-flow k&n filter system for my warrior with an outwear and taking the cover off. The main jet is 148 I believe. This is all I'm doing, everything else is stock. What size should I start at? Two up 150? I'm not in high elevation, I live in MO. Thanks for the start.

 

The stock main jet is a 145. I'd try a 150 & test ride it. at a lower elevation it should be sufficient for your present set up unless you plan to modify the air box. Mikuni uses two different type main jets in Warriors; a rond head with a screwdriver slot, and a smaller hex head. I'd pull the one you have before buying any to see which kind you have.

 

If its stock its already over jetted with a 148. If your in Mo. your probably at around 2000'...
Thats elevation
I wouldnt touch the main jet, till I rode it with the new filter installed...
Im at sealevel with a highly modded Wolverine and I run a 140 main in a 36mm carb...
Hope this helps