Abstract: A fuel economizer system and fuel flow control valve arrangement for an internal combustion engine having a fuel supply tank, a main fuel supply line connecting the tank to the carburetor inlet of the engine, and a fuel pump in the supply line for delivering fuel to the carburetor inlet. The control valve arrangement is located in the fuel supply line between the fuel pump and the carburetor inlet, and includes a first control valve which is automatically incrementally adjusted between closed and open position by a diaphragm motor which is operatively connected to the intake manifold of the engine such that changes in vacuum in the intake manifold automatically adjust the control valve to proportionally increase or decrease the supply of fuel to the carburetor inlet.