I took the car to it's yearly check-up which includes an emissions test and it barely passed. The mixture was way too rich, so I have to do something about it. The only real symptoms you get is backfiring when you step of the gas after accelerating when the engine is COLD.

Since the carb is electronically controlled, shouldn't it adjust the mixture by itself? The car is not giving any codes, the oxygen sensor is about a year old and the car is pretty much stock. The only "mod" is a K&N filter.

The ignition system is in good shape (supposedly). Cap, rotor and wires were changed about 1 year ago, plugs 6 months old. Where should I start looking for the problem? And can you adjust/should you adjust the mixture through the carb, or is the old piece of crap just worn out?

 

To answer your first question, yes the carb adjusts the mixture through the mixture control solenoid based on signals from different sensors (coolant temp., O2, and Throttle position).

Start looking at the simple things first before tearing the carb down. Check TPS voltage, check for proper operation of the MCS, replace the O2 sensor if it's been awhile.