Abstract: Disclosed is a trouble warning device for an air-fuel ratio sensor mounted in an internal combustion engine. The trouble warning device comprises a comparator which compares the output voltage level of the air-fuel ratio sensor with a reference voltage whose level is higher than the output voltage level of the normally operating air-fuel ratio sensor and an indicator to give warning of trouble in response to the compared result. By using this trouble warning device, correct detection of trouble and reliable warning of trouble in the air-fuel ratio sensor can be obtained.

Abstract: A carburetor for minimizing the variation in the ratio of fuel contained in the fuel-air mixture due to fuel evaporation within the float chamber. The carburetor has an air passage providing communication between the float chamber and the air intake pipe at a location upstream of the throttle valve. A further air passage provides communication between the float chamber and the air intake pipe at a location disposed downstream of the throttle valve, which further air passage contains a throttle therein for controlling the flow therethrough.