It is a line from the bowl up to the top of the air filter side of the cab with a port that injects gas in the middle of the carb at about a little after 3/4 so basically you under jet your main jet and it as an adjustable jet on this line that allows you to control your top end jetting. Not to mention atomizes the fuel better since it is in the center of the carb. Here is a picture of what it is.
http://www.1dirracing.com/gallery/di...ch&cat=0&pos=9
I have this on my banshee I only have one per carb they have a setup for 2 per carb. It is similar to the dial-jet but I couldn't say I've never used a dial-a jet. I have to say my banshee has a second powerband. My buddy that rides the quadzilla even was impressed by it and is having 2 installed on his carb for his zilla as we speak.