The primary disadvantage of a float carburetor is its tendency to ice up.
Here's a more detailed explanation:
The float carburetor design requires fuel to be discharged at a point of low pressure. This means the discharge nozzle must be located at the venturi throat (the narrowest part of the carburetor), and the throttle valve must be positioned on the engine side of this nozzle. This arrangement creates conditions that are ripe for carburetor icing.
Why Icing Occurs:
The process of fuel vaporization absorbs heat. This significant temperature drop within the carburetor, combined with moisture in the air, can cause ice to form. This ice can restrict airflow and fuel flow, leading to engine problems such as:
- Reduced Engine Power: Ice buildup can reduce the amount of air entering the engine.
- Rough Running: Uneven fuel-air mixture distribution can cause the engine to run erratically.
- Engine Stalling: Severe icing can completely block airflow, causing the engine to stall.
Factors Contributing to Carburetor Icing:
- Ambient Temperature: Icing is most likely to occur when the outside air temperature is between 20°F and 70°F (-7°C and 21°C), particularly when humidity is high.
- Humidity: High humidity provides the moisture needed for ice to form.
Mitigation Strategies:
While the icing tendency is a significant drawback, there are methods to mitigate it:
- Carburetor Heat: Directing heated air from the engine exhaust manifold into the carburetor can prevent or remove ice buildup.
- Alcohol Injection: Injecting alcohol into the intake air stream can lower the freezing point and help prevent ice formation.
In summary, while float carburetors are relatively simple and inexpensive, their susceptibility to icing is a major limitation, especially in certain atmospheric conditions.
