Curious that nobody has chosen this option. My 21 had 128 mains. Was running lean, and I wanted to stagger the jetting (smaller in the rear cylinder), so ordered one jet each of 145 through 155. Wasn't really sure if that would be too much, or not, but needed a starting point regardless. Put the 148 in the front cylinder, and 145 in the rear. Kept the lid on the airbox (all of this is using stock-style filter). Wouldn't pull past 7k. Read some forums, popped off the airbox lid (no other changes), and ran it down the street again. WOW! What a screamer.
In my mind, I'm getting more airflow than drilling holes, still filtering the air, and a lottttt more noise.
Thoughts? Aftermarket pipes. Otherwise, who knows? This poor bike led a hard life before I got it....