new air flow in or out!
If you change the airflow in or out, rejetting the carbs will be needed. If you are thinking about opening up the intake of air, do it before you rejet the carbs so that the rejetting will include the mods to intake of air. I saw a article in the forums about taking off the airbox and cutting a set of 3 holes in the very front of the airbox part that bolts on between the cylinders. You will need to take the air cleaner cover off and the top that holds the air cleaner to get to the box. I did it to my 1100, and its a definite improvement on air flow, and its hardly noticeable also. I Cut a oblong hole instead and bolted screen in behind the hole at top and bottom. then I superglued it along the sides of the hole. It looks great and also gives your carbs a fresher airflow instead of the hot air off the motor.
I would suggest it to anybody thats looking at a increase in performance, its not a big increase but it keeps the bike looking stock, and its hardly noticeable behind the air cleaner.