• If the idle RPM is too high then the idle mixture isn't going to respond. The RPM has moved past the idle circuit. Adjust the idle as per manufactures specs.
• Too much air, or too much fuel? Too much fuel will usually show up with a gassy smell.
• You may have a restriction somewhere. Remove the idle mixture screws and make sure they blow through to the bore and then to the venturi. The very small passages are usually the idle vent passages. Inspect the throttle body gasket carefully to make sure it isn't covering up a vacuum passage. The 4 jets used multiple types of gaskets and they are easily mixed up. Blow through every passage to make sure they are clear.
• Check around for vacuum leaks, intake, carburetor mount, vacuum lines coming off the carburetor, or intake. Use spray carburetor cleaner to spray around seams. A change in RPM indicates a leak.
• Too much fuel - too much fuel entering the float bowl can cause air/fuel mix problems. Check the float level.
• Look down the carburetor while at idle RPM. If you see gas dribbling out of the venturi then you have a problem with the discharge. Make sure the main discharge has the check ball and it seats. There should also be the spring and the T installed above the check ball.

Bottom line is that the idle mixture is telling you there is a problem with the carburetor, either getting too much fuel, or too much air.