i have a 86 montero, and was curiouse how come my check engine light never comes on, even when i unplugged the o2 sensore. then i realized i dont have one. how do you know when somethign goes bad like the o2 sensore. and also on a carborated motor, how does the o2 sensore adjust the mixture?

I don't think the carb engine has any error codes you can read without a factory scanner, and maybe not even then. There's an engine computer that reads the O2 sensor and the water temp sender and the rpm signal, and runs a solenoid jet in the carb to control the mixture. There's two sets of main jets in the carb for the primary barrel. One's a plain vanilla venturi vacuum jet that provides most of the fuel, and the solenoid valve jet adds the proper fuel trim amount from the lookup table in the computer for the given sensor readings. You can only test the sensors with electrical meters to see if the output is in spec for the given engine conditions, and use a sniffer to read the exhaust gases to see if it all works.