It is an 02 sensor. It just tells the computer to modulate the air diverter valve so that it will modulate air being injected to the exhaust manifold. That's all it does since the carb doesn't do any adjustments other than manual screw adjustments. If the o2 isn't working the air injection may run all the time and causse your NOX to read high and fail. But if your o2 sensor is good then be sure that the electric diverter valve is good and working too.

thank god u could explain this. everyone one else always said generally on cars/trucks with these they have some electronic metering in the carb. but with the numers im getting i do not think its bad. and i dont even see a NOx measurement on my test sheet