Does it idle smooth? Have you put a vacuum gauge on it. I might lean towards a bad plug or wire, but then again you said it got 20 MPG on your road trip.
Idles smooth around 500rpm ............ I am not trying to drag this thread out just looking for a few clues ..Thanks
Avoid that RPM range and you're good to go! It will either go away or get worse, then and only then you'll know what gremlins are lurking. 500 rpm idle, not too radical a cam in that one.
One more idea before I call it quits, do you have vacuum advance? Is there any chance you connected it to a different port when the new carb was installed? The difference between ported and non ported vacuum may affect how the engine acts loaded at low RPM but I have to admit I have not had a lot of experience with it to be sure.
Alternator? Water pump? P/S pump? A/C compressor? Belts deteriorated, delaminated, broken cord? Cracked pulley? Run it without the accessory belt(s) for a short time and see if anything changes. Rodents build a nest in the bellhousing during 4 years in storage?
After revewing all of this ..I have come to realization it mostly the carb and have been in contact with edelbrock to get a adjustment on the meter rods.
If it's still there afterwards, unbolt the torque converter and slide it backwards... Then get in the car and rev and see what happens.
Now back to the carb , are all the vacuum line hooked up in their correct place and are any of the lines cracked ? Do you have a friend that has another carb that you can install to see if that is the problem ?
Now back to the carb , are all the vacuum line hooked up in their correct place and are any of the lines cracked ? YES Do you have a friend that has another carb that you can install to see if that is the problem ? NO
I have seen engine rpm vibration problems with torque convertors, but typically the rpm range for that vibration would be at a higher rpm. Are your motor mounts stock rubber type or the "newer and better", harder urethane?