Abstract: A carburetor is provided with an air bleed passage connected to the main fuel well; the passage being controlled by a solenoid opened, normally closed valve; the solenoid being electrically connected in series arrangement with a venturi vacuum actuated, normally closed switch and a wide open throttle (WOT), normally open switch closed by movement of the throttle valve to a wide open position, the electrical circuit being completed at low mass air flows, WOT operation to open the air bleed line and lean out the air/fuel ratio of the mixture charge; the electrical circuit being broken when venturi vacuum reaches a predetermined level indicating maximum horsepower will be better obtained by a richer air/fuel ratio.