This question is concerning a mod that one of my riding buddies is doing to his carb off of his 2001 520. He sent his carb to guy who specializes in high end carb mods. What was done was the inlet air horn was removed and new machined piece was installed in its place. In this piece is an adjustable metering valve that feeds fuel from the bottom of the float bowl into a tube that sticks into the center of the carb throat making another fuel circuit. He also lowered the main jet to a 155 and backed off the accel pump. We will find out how this works this weekend, but I was curious if anyone had heard of anything like this.