EETC Carburetor Service and Repair 1 — Questions and Answers
Question 1: What is the primary function of a carburetor in a small engine?
- To cool the engine during operation
- To mix air and fuel in the correct ratio for combustion (Correct answer)
- To generate electrical current for the ignition system
- To regulate oil pressure throughout the engine
Correct 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.
Question 2: What component in a float-type carburetor controls the fuel level in the bowl?
- The main jet orifice
- The venturi tube diameter
- The needle valve and float assembly (Correct answer)
- The throttle plate position
Correct 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.
Question 3: What is the stoichiometric (ideal) air-to-fuel ratio for gasoline combustion?
- 10:1
- 14.7:1 (Correct answer)
- 20:1
- 8:1
Correct answer: 14.7:1
A 14.7:1 ratio provides just enough air to completely burn all the fuel, minimizing unburned hydrocarbons and emissions.
Question 4: Which carburetor circuit provides fuel to the engine during idle operation?
- Main metering circuit
- Choke enrichment circuit
- Idle circuit (Correct answer)
- Accelerator pump circuit
Correct 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.
Question 5: What physical principle draws fuel from the bowl into the airstream inside a carburetor?
- Fuel pump pressure pushing fuel upward
- The venturi effect creating low pressure at the narrowed passage (Correct answer)
- Float buoyancy forcing fuel through the main jet
- Gravity feeding fuel from a raised bowl
Correct 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.
Question 6: What material is most commonly used for small-engine carburetor body construction?
- Stamped steel sheet metal
- Stainless steel casting
- Zinc die-cast alloy (Correct answer)
- Machined brass
Correct 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.
Question 7: What is the purpose of the emulsion tube found in some carburetors?
- To filter debris before fuel enters the bowl
- To introduce air into the fuel stream and atomize it before the venturi (Correct answer)
- To control the choke plate opening angle
- To regulate throttle response at high speed
Correct 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.
EETC Carburetor Service and Repair 1
What is the primary function of a carburetor in a small engine?