10.12.2006, 00:00
Carburetor Icing
Carburetor icing occurs when the intake air is chilled below the freezing point of water by evaporation of the gasoline in the carburetor. The ice forms on the throttle blade and in the venturi and can interrupt carburetion, causing the engine to stall.
Icing can be acute when the air is moist (70 percent or higher relative humidity) and the ambient temperature is between 2°C and 13°C (35°F and 55°F). These weather conditions are common during the fall, winter, and spring in many parts of the country and they can last well into the summer in some coastal regions. Carburetor icing is not a problem when the intake air temperature is below freezing because then the air is too dry.
The extent of carburetor icing does not depend on the weather alone. It also involves carburetorand vehicle design and the mechanical condition of the engine — in particular, those components that affect warm-up time, like thermostats, automatic chokes, intake air heaters, and heat risers. And it also involves gasoline volatility. The 70 percent evaporated temperature in the distillation profile is a good index of the tendency of a gasoline to cause carburetor icing — the lower this temperature, the more severe the icing.
Carburetor icing is not as big a problem as it used to be. For emission control reasons, most carbureted engines built since the late-1960s have been equipped with intake air heating systems, which generally eliminate carburetor icing. Today the problem is not large because vehicles with carburetors mostly have been replaced by fuel-injected vehicles.
Carburetor icing occurs when the intake air is chilled below the freezing point of water by evaporation of the gasoline in the carburetor. The ice forms on the throttle blade and in the venturi and can interrupt carburetion, causing the engine to stall.
Icing can be acute when the air is moist (70 percent or higher relative humidity) and the ambient temperature is between 2°C and 13°C (35°F and 55°F). These weather conditions are common during the fall, winter, and spring in many parts of the country and they can last well into the summer in some coastal regions. Carburetor icing is not a problem when the intake air temperature is below freezing because then the air is too dry.
The extent of carburetor icing does not depend on the weather alone. It also involves carburetorand vehicle design and the mechanical condition of the engine — in particular, those components that affect warm-up time, like thermostats, automatic chokes, intake air heaters, and heat risers. And it also involves gasoline volatility. The 70 percent evaporated temperature in the distillation profile is a good index of the tendency of a gasoline to cause carburetor icing — the lower this temperature, the more severe the icing.
Carburetor icing is not as big a problem as it used to be. For emission control reasons, most carbureted engines built since the late-1960s have been equipped with intake air heating systems, which generally eliminate carburetor icing. Today the problem is not large because vehicles with carburetors mostly have been replaced by fuel-injected vehicles.