If you do anything to the air box on the 660, you will need to rejet. I tell you from experience. I cut the top of my lid off and went up on the jetting and was still lean. I then put a stock air-box lid on though I had a small hole in the side of my air box, went back to stock jetting and was still lean. The air-box is so resrtricted that the first time you put a hole or anything in it, it let's so much more air in.