I run about 12 for the carb and 8-10 for the pressure pipe. I coil up the pressure line and ziptie it so it stays in a coil. I've noticed a smoother tune with more pressure line.
I have no idea how long its supposed to be but I run like 15inches in carb and as short as possible wile still not having kinks on the pipe and for some reason it works great for me!
Having a longer pressure line tends to make the tune more even as it absorbs some of the pressure from the exhaust pulse. It makes it more of a constant pressure instead of a "pulsing" pressure.