Lowtimer is correct in saying that cars with cats need Fuel-injection, although not all have water heated manifolds. Cats are very temperature sensitive, if they are too cold, they don't work. Too hot - they melt. If the mixture is too lean, they melt and if its too rich - they melt. Carbs just aren't accurate enough.
Inelegant aero - cars can suffer from 'hot air uptake' where the air charging system draws in hot air from the engine compartment and there is a power loss. Cold air must then be ducted towards the air intake spout.
Engines thrive on cold, damp air. The colder it is, the denser it is so a greater fual/air charge is drawn into the cylinders. The dampness in the air is converted to steam and expands violently when the charge burns. You may have noticed that your car performs better under these conditions.
Changing the subject a bit - there are commerically available Carb-Ice Detectors that will light a bulb in the cockpit when ice is detected. Why? Why not use the current that lights the bulb to close a relay that switches a motor that operates a flap that ducts hot air to the carb? Any ideas?
