I have tried it out and the fatory drivers I see at races alll use a pressure line but they might have tried running w/o one before, so I wouldn't go as far to say that they don't use them. It does make the engine smoother, you need to richen the main needle at least 1/4 turn but more like 1/2 or little more and bottom like 1/4 turn. I only ran it long enough to get it tuned good but would asume that it would get better fuel milage since it's just drawing in the fuel it needs and not being forced any excess fuel. One bad thing is that if the motor stalls you can't put finger on pipe to prime or force cool fuel into the engine to get it started again.