The misfiring-like feel goes away when it's revved over 2000 rpm. At idle the engine shakes and a little above idle it gets even worse. Over 2000 rpm the engine is smooth and the car has excellent pickup (no knocking, pinging, hesitation, etc.). The car was tuned up by the previous owner (I just bought the car), but I took everything apart to inspect (looked at the cap, rotor, wires, plugs, etc.) and tried cleaning the spark plugs (which are very black with soot, but otherwise appear to be almost brand new), but that didn't really help much. I'll check the air cleaner position and replace the plugs with new ones and try readjusting the carbs from there.