Boy, does my son's slant run crappy!

Aaron came home from college over the weekend to leave his slanted '74 Dart Sport with me to diagnose and hopefully fix. He has been complaining for several weeks about how badly it has been running.

I got a good dose of it this morning on my way to work. It fired right up, idled fine through a short warm-up period, and had quick throttle response - so far, so good. I backed it out of the driveway, eased down the street to the stop sign, made the turn and drove four or five blocks to the next stop at a leisurely pace.

Then it started...
I slowed down to get over a rough RR crossing and for the next acceleration it began sputtering. I eased off the throttle for the length of the block to the stop sign, and it idled OK while stopped. I made my turn, and for the remainder of my 10-mile trip to work, it sputtered each time I pushed the throttle. The best way I can describe it is that it acts like a 4 HP Evinrude boat motor - it literally "sputters".

It is a "Super Six" with a Carter BBD 2-bbl and MOPAR electronic ignition. Just before Aaron's semester at A&M began, we had to have it worked on for carburetor problems. At that time, it would start but only run if you kept pressure on the throttle. Otherwise, it would bog down and die. It turned out that one of the brass tubes in a venturi had fallen out and wasn't siphoning fuel as it should - the carb was running too lean.

This time, it does not act the same way - it idles fine with no bogging. Are we looking at a carburetion issue, or could it be ignition? Or something else?

Any ideas are welcome,
Jerry