traditionally:
if your carb is too big, the engine will run lean.
if the carb is too small the engine will run rich.
you may have ignition wire issues as others have pointed out since your popping only from one bank.
you can check fire easy using a timing light, use it on all 8 wires and watch the strobe it can be easy to spot one of them not firing or misfiring. if you have a timing light with adjustable timing then you can really check to make sure all the plugs are firing. I had a situation with a bad Pertronix magnetic sleeve were 1 cylinder was no longer firing, i replaced the sleeve under the cap with a new one and the problem went away.
what carb CFM did you run before the new 600CFM?
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When running right the extra carbon should burn off at highway speed. that is why the old way of checking a tune was to drive 55mph and shut the engine down pull a plug and check it this would give you uncontaminated results of how the Cruise mixture was set. idle always introduced extra carbon on the plugs and made reading them a pain.
if you have a lot of carbon built up then the engine timing will change as the carbon burns off. this can drive you nuts. the engine will retard timing as the build up burns off so you have to check the timing again after the first long drive.
I had a major rich condition in my engine due to bad ignition wires which fowled the plugs with heavy carbon,, when i changed the wires and the car ran decent, i had 18 degrees of initial timing i went on a 40 miles trip i came back the plugs were white and i had lost 8 degrees of timing and the car had settled at 10 degrees of initial timing, all from the carbon burning off and confirmed with my timing light.
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If you rev the motor fast from idle is it popping also? you may need to play with the accelerator pump settings