As Steve said, I would connect a vacuum gauge to it and assuming all else is ok (plugs, ignition, etc.), lean it out on all 4 corners of the carb to maximize the amount of vacuum you can get at idle. I have a QuickFuel 600 mechanical secondary carb (new 2 years ago) and it is quite nice and no raw fuel smell beyond what any 53 year old muscle car smells like.
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