Abstract: A method and apparatus for controlling an air-fuel ratio for an engine, in which a closed-loop control and an open-loop control are performed selectively in accordance with the operating condition of the engine. The closed-loop control determines an air-fuel ratio of the mixture to be supplied to a combustion chamber on the basis of the oxygen concentration within the exhaust gas. The open-loop control determines an air-fuel ratio of the mixture by modifying the air-fuel ratio determined in the closed-loop control in a manner that the former one is lean by a predetermined ratio than the latter one.

Abstract: An air flow rate measuring apparatus in which an air flow sensor whose electric characteristic varies with the rate of air flowing by the sensor is supported on a heat-insulating support member and located in a bypass tube provided in the vicinity of the main venturi of an internal combustion engine, whereby the air flow sensor is isolated from adverse thermal influences so as to reduce an error in measuring air flow rate.

Abstract: An air flow rate measuring device has a by-pass passage branched from a main air passage leading to an engine, and heat wires provided in the by-pass passage. The inlet of the by-pass passage is positioned at the upper end of a venturi tube disposed in the main air passage, shaped annularly, and opened to the main air passage so that the air at the inlet can be subjected to the dynamic pressure of the main air stream. The outlet of the by-pass passage also is annularly formed and opened normally to the main air stream in the main air passage. The flow rate of air sucked into the engine is measured by the heat wires subjected to air flow taken in the by-pass passage.

Abstract: An altitude compensating device for carburetors has an air metering valve in fluid communication with the fuel passage of the carburetor and a pressure-sensitive bellows adapted to drivingly control the air metering valve such that the flow rate of the compensating air is increased as the altitude increases. A closed control air chamber is defined at the upstream side of the air metering valve. Venturi vacuum around the venturi portion of the intake passage of the carburetor and air are introduced into the control air chamber so that the pressure in the latter is reduced below the atmospheric pressure with an increase of the intake air flow rate to the engine and the compensating air is decreased to eliminate undesirable low concentration tendency of the mixture.