Some models are equipped with an Electronic Feedback Carburetor (EFC) System which is designed to convert Hydrocarbons(HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx) into harmless substances. An exhaust gas oxygen sensor generates an electronic signal which is used by the Spark Control Computer to precisely control the air-fuel mixture ratio to the carburetor.
There are two operating modes in the EFC system:
- OPEN LOOP-During cold engine operation the air-fuel ratio will be fixed to a richer mixture programmed into the computer by the manufacture.
- CLOSED LOOP-The computer varies the air-fuel ratio based on information supplied by the oxygen sensor.