Let's follow this guide generally - it's for a multi carb multi cylinder bike but it gives you a place to start -
http://www.motorcyclecarbs.com/Motorcycle_Carburetor_Jetting__W7.cfmfollowing the above refference "generally" - the pipe you have installed is more like a free flow than 4 into 1 where you get a scavenger effect do let's call it
1 size for the pipe
1 size for the drop in K&N
and 1 size because it so d@mn lean in the first place!
I would do (3X2.5) + 130
137.5 main is where I would start and would buy a 50.0 pilot but maybe not install it until i found out where i ended up on the mixture screw - but if jet's are hard to get i'd also buy a 140 main - just in case.
I would also do the sparkplug door mod (just leave out the rear bolt on the left hand chrome head cover)
so I could pull the sparkplug to see what color it was running.