Factory Holley fuel pressure regulator carb fuel control hot rod muscle carHolley fuel pressure regulator, often used to control fuel flow to carburetors. Function: These regulators precisely manage fuel pressure from the pump to the engine, preventing overloading of the needle and seat which can cause flooding. Specifications: Models like the 12 804 are adjustable, with a typical factory setting of 2. 8 PSI, but can range from 1 to 4 PSI. selling as pictured. more than welcome to pick up at shop in butler pa & save