Make sure your idle is set high enough. Your idle screw is what prevents the slide or barrel from fully closing while braking. It actually physically prevents it from closing all the way. So you want to make sure it's set right. You can check it without running it. Just pull the air cleaner and operate the throttle with the radio. You can look in the barrel and watch it open and close. If it fully closes while pushing on the brakes, it's set too low. Make sure you have your 1mm gap.