Also note that carb heat and manifold heat aren't really the same thing. The manifold heat is to keep any puddled fuel droplets in the intake from building up too much by flashing them back into vapor. Carb heat takes care of the frost formed around the throttle plate due to venturi temperature drop. Some cars have carb heat as well- its usually a heat stove around an exhaust manifold connected to a flapper in the air cleaner snorkel.
