[piecesparts]

Look at it this way, the line to the bottom of the carb has a negative pressure or a vacuum on it, caused by the cylinders sucking in air and fuel into the cylinders. The one to the air cleaner has a positive pressure to it, since it is connected to all of the free air space above the venturis in the carburetor. That is why the two lines are different. By running your PCV this way, you are sweeping the spent gasses and oil fumes from your engine's crankcase and keeping it from becoming pressurized and blowing oil out of the seals and gaskets. This makes your engine run with less resistance (windage) inside it.