Changing the plugs is critical, too. I'm running Bosch Platinums and they run much cleaner than AC or AC Rapidfire.

Also make sure the exhaust manifold heat riser valve either works freely or is wired open.

The two barrel carb flows more fuel than a four barrel until you mash the pedal. If most of your driving is around town, the two barrel is a good carb. It won't cut it for drag racing. One of my best sleeper cars was a '71 Impala with a 400 2 bbl that was very fast off the line.