At the back of the rear of the cylinder on top of the case is a black hose leading to the airbox , assuming it has not been replaced with an aftermarket breather , if it has , then just clean the thing up !

2005 Model . Two Fast Eddy stickers , a bell and a clock . She's Lola . She tinkles and keeps time . http://s649.photobucket.com/albums/uu211/britbike05/