I hunted for these answers quite a bit before I started this ... THANK YOU VERY MUCH FOR ANY HELP YOU CAN LEND WITH THESE. -=-=-=-=-=-=-=-=-=- A Honda 650L is Factory lean (I believe this is correct). [i live & ride at 5000ft level and will ride higher at times.] With that said.... How is the determination made for the jetting the bike is supplied with? Could the assemblers of the bike (Dealer) be jetted with appropriate ones for the area in which it was first assembled? And WHY the F*&! is it lean to begin with? (IF indeed the 650L is assembled lean) Does pulling the smog affect jetting (would alterations be necessary IF the jets are fine as is; if the smog is pulled)? Is back pressure necessary for better performance? If a bike is altered for better breathing does this limit back pressure to a point where adjustments are required? Should all mods be done first and jetting last? Would any alteration in breathing & back pressure affect jetting so that pulling smog, exhaust alterations, air filter need to be done and finalized prior to beginning jetting? (This seems logical but is there any reason for this NOT to be true?) ARE performance exhausts mainly hype in the 650-L application [if the uses are in line with the design of the bike]?