Air box lids have been very frustrating for many years and for many people. If you leave them on, it
hinders air flow and power. If you take them off, you have a much greater chance to get water or mud in
your air filter and engine. On the 400ex, the lid plays a part in keeping the air box rigid and when you
remove the lid, the front of the air box can drop and pull the air boot loose from the carb when landing
off big jumps. This rubber velocity stack that I use has a lip that curves out in the top to help deflect
water. If you are carefull of where you install it in the lid, it can also direct any water that comes in past
the air filter and out the bottom of the box. To install it you drill a 2 inch hole in the lid with a 2 inch hole
saw and simply push it in place. It has a lip above and below the lid to keep it in place at all times. On
most bikes one is enough but I prefere 2 on the Yamaha Banshee. I sell them for $20.00.