Carburettor Icing

A common cause of sudden loss of power or complete cutting-out of the engine—usually within a few minutes of starting from cold—is "icing" of the carburettor. This occurs during cold, damp weather, when the refrigerating effect of the evaporating fuel is sufficient to freeze the moisture in the air which is drawn into the carburettor, causing deposits of frost or soft ice around the jet and the edge of the throttle plate. The trouble is seldom experienced during really cold, frosty weather, when the air is relatively dry. An air temperature of around 50°F (10°C) is most likely to create carburettor-icing conditions.




The risk of icing can be reduced by setting the carburettor air intake to the warm-air position {see page 40). If icing does occur, the engine can sometimes be persuaded to pick-up by quickly opening and closing the throttle a few times in order to break up the ice or frost in the intake. In any case, the engine will generally re-start without difficulty if it is allowed to stand for a few minutes, thus allowing the carburettor to soak up sufficient warmth from the engine to melt the ice.