If Reg454 and Bikeguy's stuff didn't help (esp. backing out the idle screw) grab the cable housing where it goes into the top of the carb and pull up. You can feel the carb slide go up and down. Now when it hits the bottom is there any slack in the cable? You should be able to move the housing up and down about an 1/8" before you move the slide. I had to back my idle off too when I put my pipe on. It's making the flow a ton better. Your old exhaust was restricting and slowing the idle.