One other purpose
Additional power can be realized over many sport type engines if a Perry/Varsane/Conley pump is used with a matching Perry 'pump' carburator. Many engines are limited in their venturi size by the need to provide suction to help in fuel draw. The Perry pump type carb will have a considerably larger venturi for any given stock application and produce more power. Perry does make pumped and unpumped carbs and the pump type will not effectively work without the pump.
John