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Fuel Metering Systems: Powerplant practice questions

Five original questions on fuel metering systems, each with the answer, an explanation and an FAA-H-8083-32B page reference.

1. What happens to air as it passes through the throat of a carburetor venturi?
  1. Velocity increases and pressure drops
  2. Velocity drops and pressure increases
  3. Both stay the same
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A. Velocity increases and pressure drops The lower pressure draws fuel into the airstream.

Reference: FAA-H-8083-32B, Ch. 2, p. 2-5

2. Why does a float carburetor have an accelerating pump?
  1. To keep the engine from accelerating slowly or stumbling when the throttle is opened quickly
  2. To feed fuel at idle only
  3. To lean the mixture at cruise
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A. To keep the engine from accelerating slowly or stumbling when the throttle is opened quickly It is a small piston pump worked through linkage by the throttle.

Reference: FAA-H-8083-32B, Ch. 2, p. 2-13

3. What is another name for the carburetor power enrichment system?
  1. Accelerating system
  2. Economizer or power compensator
  3. Idle cutoff
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B. Economizer or power compensator It enriches the mixture at high power settings.

Reference: FAA-H-8083-32B, Ch. 2, p. 2-8

4. When checking idle mixture by moving the mixture control toward idle cutoff, what rpm rise is typical before rpm drops?
  1. 10 to 50 rpm
  2. 200 to 300 rpm
  3. No rise at all
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A. 10 to 50 rpm The rise varies with the installation.

Reference: FAA-H-8083-32B, Ch. 2, p. 2-30

5. Which carburetor system supplies fuel at all speeds above idling?
  1. Main metering system
  2. Idle system
  3. Idle cutoff system
Show answer

A. Main metering system The other systems (idle, accelerating, mixture control, idle cutoff, enrichment) work with it.

Reference: FAA-H-8083-32B, Ch. 2, p. 2-7

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What does the Powerplant test cover on fuel metering systems?

The Aviation Mechanic Powerplant ACS lists fuel metering systems as one of its areas. The FAA reference for this material is FAA-H-8083-32B.