Syncing carbs is when you make sure the butterflies of all the carbs open and shut at exactly the same time. It basically means the bike will rev cleaner and return to idle quicker and it will idle smoother. The issue with syncing is that it must be done when the engine has been warmed up. On the ZXR, the adjustment screws are hard to get to, so wear something on your hands to avoid being burnt. This video is dealing with another bike, but inline fours like yours are all fairly similar. You sync the carbs in pairs...1&2 + 3&4 and then you balance those pairs to each other. Other inline fours may have a different process, but that is the correct procedure for the ZXR250A. I know, I've done it many times.