I know this is an old model, so therefore this is old news. I just wanted to point out to those of you who have an S4RS that the air box lid design is extremely restrictive. The opening area into the air box is much smaller than the area of the injectors. I don't recommend running no lid at all , especially in wet or dusty conditions, because of the location of the air box in relation to the fuel tank. If you have not modified your air box lid, though, you need to . I opened up the front of mine on either side of the factory hole. This wouldn't be the best place if you ride in the rain. Holes down the sides might be a better alternative for a daily driver, but they need to be substantial to eliminate restriction from the lid. The air box volume itself is also too small, but there's no room for a properly sized one. An aftermarket low restriction filter is about all you can do to help, but you need to do both. Another reason to go aftermarket on the element is that the stock paper filter will not handle any moisture without becoming more restrictive.