hey mate, called a restriction, there are 2 on the drd´s pipe, the one u described being the one right at the start of the pipe, second is the tube that sticks out just before the expansion chamber, called a resinator pipe. cut it off, weld over hole and voila, one quick bike. you will need to rejet your carb otherwise you blow up engine, i believe it needs about a 93 main jet. then put the cir clip one needle up on mid range adjuster. you will also need a bigger front sprocket, i recomend a 13t, good compromise between speed and accletation. you also need to buy a standard sprocket retainer of the older senda. my mates bike does 55 like that, i have a gianelli pipe and i get 60 on the flats. ope that helped a little