Folks, I recently picked up a 99 WR400, YZ timed, with stock open pipe. The bike runs flawlessly! I purchased a PMB insert to reduce the noise a bit. While running with the insert installed, I have noticed the following: It does silence the engine! It does however, backfire from the exhaust on deceleration. This is not a machine gun pop but an occasional backfire. It occurs when decelerating (throttle shut off) from high rpm. My question is... Rather then re jet the carb, does anyone have experience drilling out one or more of the partially drilled holes in the PMB insert? I understand this will increase the noise factor a bit but am wondering if a balance could be achieved? I must admit, I do not prefer to run a corked engine but am trying to quiet it down so as not to be potentially offensive. Appreciate your thoughts Bob!