Carburetor Service and Repair Flashcards

What is the primary function of a carburetor in a small engine?

Answer: To mix air and fuel in the correct ratio for combustion

The carburetor mixes air and fuel in the proper ratio so the mixture can ignite and combust efficiently in the cylinder.

What component in a float-type carburetor controls the fuel level in the bowl?

Answer: The needle valve and float assembly

The float rises with the fuel level and pushes the needle valve closed to stop fuel flow and maintain the correct bowl height.

What is the stoichiometric (ideal) air-to-fuel ratio for gasoline combustion?

Answer: 14.7:1

A 14.7:1 ratio provides just enough air to completely burn all the fuel, minimizing unburned hydrocarbons and emissions.

Which carburetor circuit provides fuel to the engine during idle operation?

Answer: Idle circuit

The idle circuit meters fuel when the throttle plate is nearly closed and engine speed is low, where the main circuit cannot produce enough vacuum.

What physical principle draws fuel from the bowl into the airstream inside a carburetor?

Answer: The venturi effect creating low pressure at the narrowed passage

Air accelerating through the venturi's restricted passage drops in pressure, creating a vacuum that pulls fuel up from the bowl.

What material is most commonly used for small-engine carburetor body construction?

Answer: Zinc die-cast alloy

Zinc die-cast alloy (Zamak) is lightweight, corrosion-resistant to fuel, and easily cast into the complex internal passages a carburetor requires.

What is the purpose of the emulsion tube found in some carburetors?

Answer: To introduce air into the fuel stream and atomize it before the venturi

The emulsion tube bleeds air into the fuel before it exits the main jet, breaking the fuel into fine droplets for better atomization.