Abstract: Two embodiments of air/fuel ratio adjusting systems for gaseous-fueled internal combustion engines. In each embodiment, a pressure regulator supplies regulated fuel in gaseous form from a source in which it is stored in a liquid form to a charge former that has a fuel control device such as a needle valve. The air/fuel ratio is maintained constant by mixing atmospheric air with the fuel before the charge former fuel control device under the control of an oxygen sensor in the exhaust system. In one embodiment, an enrichment system is also incorporated for supplying enrichment fuel under acceleration or cold starting conditions.