Another reason for the air box, often overlooked by tuners, besides preventing water intrusion, is that there is less noise. After any rebuild, when I do my break in, and out of the hole water tests, since all engines are different, (especially after a rebuild, larger piston, etc, ) with the seat off, I can reach down to set the the low speed pilot screws , which is much easier to do, and impossible with the air box on. Of course I do this on calm water with no one around to annoy.