[curtis73]

It depends on the carb. Most will run fine over a wide range of settings, but depending on the carb the bench setting could be 1, 1.5, or 2 turns out from seated. Try taking them both in by a half turn or so but remember where you were.

you also didn't say if something else changed. Did you change cams, calibrations, switch carbs... A factory carb would not suddenly go out of tune. If it was running fine before, the idle mixture isn't to blame.

I would look first to the float. They get logged and sink allowing fuel to continue to pump in after the bowl is full. The extra fuel just spills right into the throats and causes rich operation.

It could also be a vacuum leak. I know it sounds counter-intuitive, but vacuum leaks can cause fluctuations in idle vacuum that make very uneven fuel distribution in the runners. The overall result is an average lean condition, but one or more cylinders run very rich and the exhaust smells like gasoline. You can chase down vacuum leaks with some starting fluid or brake parts cleaner. Spray short bursts at gasket mating surfaces. If the idle changes (smooths out, increases) then you've found a leak.

Also, some fuel pumps have one "in" and two "outs". The second out is a return to the tank. If it gets plugged or restricted, the pump will deliver more than required pressure which will overpower the float and cause a rich condition.

The idle mixture screws are designed to dance around very close to ideal tune, but wouldn't be responsible for that much of a rich condition on their own.