First of all, what's jetting and how can i tell what mine is at. Second, if I mod the air box on my xr600r do i need to mod anything else(ie jetting)? I've seen people cut open a small square on the side and then glued a screen to prevent most dirt from getting in. Should i go ahead and do this, and is it really worth it? BTW if u guys would share any other inexpensive mods i'd like to hear them. Thanks in advance.