I done this to mine a few month ago it improved throttle responce (nothing major) but its a very simple job just pop the carb off and its on the left hand side undo the four bolts then you will see a square bit sticking out this is the bit to be cut away then shave the inside edges to make it more circle like them pop back on . you might as well give your reeds a little clean aswell . but i noticed a bigger improvement when the exaust was de restricted at the flange end there is a small peice of pipe that needs taking out cost me £20 at a local garage