The job of the insulator is to keep heat away from the carburetor. The shape of the venturi inside the carburetor causes the air going into the carburetor to drop 30-40 degrees in temperature. This cooling effect can cause condensation on the outside of the carb if the humidity is high. If you have moisture in your gas tank ice can form inside the carburetor. I've had carbs ice up when it was 60-70 degrees outside. If I poured a can of dry gas into the gas tank the icing venturi problem was solved.
