Definition
A small, secondary venturi mounted inside the throat of the main venturi in a float-type carburetor. The boost venturi discharges fuel into the airstream and increases the pressure drop felt at the fuel discharge nozzle, producing more accurate fuel metering at low airflow than the main venturi could provide on its own.
Plain English
A small extra venturi sitting inside the main one in a carburetor. It helps suck fuel out of the nozzle more reliably, especially when the engine isn't pulling much air through.
Context Anchor
Seen in carburetor and induction-system discussions, especially when learning how a float-type carburetor meters fuel into the engine's intake air.
Derivation
‘Boost’ here means to amplify or strengthen. ‘Venturi’ comes from the Italian physicist Giovanni Venturi, who described how a fluid speeds up and drops in pressure when it passes through a narrowed section of a tube. A boost venturi is a smaller venturi placed inside a larger one to amplify that pressure-drop effect right where the fuel enters the airstream.
Why Pilots Care
Maintains smooth fuel flow and prevents engine hesitation or roughness at low power settings.
Grounding Statement
As intake air rushes through the narrowed boost venturi, the lower pressure there helps pull fuel into the moving air stream.
Intuition Check
Boost does not mean turbocharging or adding extra engine power here. It means increasing the carburetor's fuel-drawing effect inside the air passage.
Example Sentence 1
The boost venturi is positioned so that its outlet sits in the throat of the main venturi, where airflow is fastest.
Example Sentence 2
During low-power descent the boost venturi helped keep the mixture stable without manual adjustment.