Re: 1953 Packard, Carter Carb rebuild input and fuel filter question

Posted by Owen_Dyneto On 2008/4/20 11:39:17

The preference for filters between the pump and the carburetor is based on the changes in physical properties of liquids when subjected to positive and negative pressures. Just as your pressure radiator cap raises the boiling point of your coolant, the fuel between the pump and the carburetor inlet is under pressure, has an elevated boiling point, and is thus more tolerant to formation of vapor. Vapor lock almost never is found between the pump and carburetor. But conversely, the fuel between the tank and the pump is under a slight negative pressure and thus has a reduced boiling point and is more prone to vaporizing. To the extent that a filter in the suction line adds to the resistance the pump must overcome, you've added to the reduction of the boiling point of the fuel in that line. Now the differences may be small, often perhaps insignificant, but you can't beat the laws of physics.