Abstract: An exhaust diffusion apparatus positionable between noise level control and performance modes defining a restricted diffusion passage and an unrestricted exit port for performance operation which may be closed to effect noise level control operation.

Abstract: A gaseous fuel delivery system for a gasoline engine having a gaseous fuel delivery valve means comprising an idle fuel delivery valve and an acceleration fuel delivery valve. Means responsive to air flow through the carburetor throat controls operation of the idle fuel delivery valve. Means responsive to intake manifold vacuum controls operation of the acceleration fuel delivery valve. Electrically operable alternately open idle and acceleration solenoid valves are interposed in separate delivery conduits from the idle and acceleration fuel delivery valves. Means responsive to the opening of the acceleration fuel delivery valve opens the acceleration solenoid valve and closes the idle solenoid valve, reversing the respective valve positions on closing of the acceleration fuel delivery valve. An idle switch responsive to idle position of the throttle prevents opening of the idle solenoid valve except when the throttle is in the idle position.