Classic/Antique Car Repair: 1973 Plymouth Duster, Hesitation, plymouth duster, nox emissions

Question
I've been working on my '73 duster and can't seem to get rid of a hesitation it has in the middle throttle area. It's a 318 c.i. I recently replaced the distributor vacuum canister for the timing advance and it got a little better. The engine specs sticker under the hood says to use TDC timing. I did put on a holley rebuilt carter carb (which i found weird) about a year ago.

The hesitation used to kill the engine if I hit the gas too hard, i got used to feathering it a little. With the new vacuum can it doesn't die anymore but now has an almost constant lugging feeling I can hit the gas but it almost feels like the engine is trying to catch up with itself. Also I have been told it was ok to bypass the OSCA valve for the advance but it didn't seem to help. Could my OSCA valve need replacement to fix this or could it be idle mixture setting. There is of course column C, something I never thought of, which is why I seek your help.

Thank you,
Kevin

Answer
What is column C? Dare I ask? This car was a bear to get running right when it was new due to the emissions controls on it. 73 was the first year that the EGR valve was introduced to the world to get rig of NOx emissions. The timing of the vacuum for the EGR could never be gotten just right and there were all kinds of driveability problems. Now a few questions if you please. Does the car have an EGR (exhaust gas recurculating valve)? If the valve hooked up? Do any of the vacuum lines that were connected to the OSAC go to the EGR? When you connect a vacuum pump to the EGR can you see the shaft lift? If the engine is running and you connect a vacuum pump to the EGR and apply vacuum does the engine stall? Let me know
Brad