Secondary Butterfly valves. The idea behind it is that Kawi (and other vendors) keep them closed until a certain RPM is reached or in 6th gear. By removing them altogether and outfitting with an ECU modder such as a Power Commander, you gain significant performance.
I know many, if not most disagree but by removing the secondary throttle plates, the performance gains often come at the expense of ridability if you're super picky about your throttle response. Smaller/different shaped secondary throttle plates are the way to go if you want the performance gain and still maintain your seemless smooth throttle response. On some bikes if you have big intake passages on the throttle bodies and no secondary plates, you have to be careful not to whack the throttle open too far too fast at lower RPMs or you can "drown" the engine with too much fuel/air causing a bog.
