A control system for improving the efficiency of an internal combustion engine includes a metering unit which divides the fuel line leading to the carburetor of the engine into a plurality of branches. All but one of the branches have solenoid valves which when closed completely block their respective branches. These branches are further provided with micrometer valves which are adjustable to vary the flows through the branches. The remaining branch also contains an adjustable valve which is set such that when all the other branches are blocked at their valves, the remaining branch supplies enough fuel to maintain the engine operating at idle or up to a specific power setting. The metering unit is coupled to a sensing unit which in turn is connected to the throttle of the carburetor. The sensing unit contains switches corresponding in number to the solenoid valves in the metering unit, and these switches are closed successively as the throttle is opened. Consequently, the solenoid valves open and close in response to the throttle position, so that each branch corresponds to a specific range of throttle positions. The arrangement is such that just enough fuel is supplied at the upper end of each range to meet the engine power demands, so that the air fuel mixture for any specific range corresponds more precisely to the optimum for the range.