Fuel Metering

Question 1

What are the air/fuel mixture ratios that support combustion?

Answer 1

8:1 - 17:1

Question 2

What is the leanest air/fuel mixture?

Answer 2

17:1

Question 3

What is the richest air/fuel mixture ratio?

Answer 3

8:1

Question 4

What air/fuel mixture ratio is considered maximum power?

Answer 4

12:1

Question 5

What is Stoichiometric?

Answer 5

The perfect air/fuel mixture in which both ingredients can be used up completely

Question 6

What is the stoichiometric ratio?

Answer 6

15:1

Question 7

What is the hottest air/fuel mixture?

Answer 7

Stoichiometric

Question 8

What is the richest mixture ratio?

Answer 8

Idle mixture
(Because of poor air flow)

Question 9

What is the SECOND richest mixture ratio?

Answer 9

Take off ratio
(Extra fuel is needed for cooling)

Question 10

What is the leanest fuel/air mixture?

Answer 10

Cruise mixture
(Engine is running at reduced power & higher altitude)

Question 11

What 2 reasons are why engines are shut down with the mixture control?

Answer 11

To prevent the un-burnt fuel from
washing away the oil film off the
cylinder wall
&
Safety (no accidental start ups)

Question 12

What 3 instruments are used to monitor engine power?

Answer 12

Manifold Absolute Pressure (MAP) - airflow

Fuel Flow

Tachometer (RPM)

Question 13

Where can manifold pressure be taken?

Answer 13

Anywhere after the throttle valve or before the intake valve

Question 14

The manifold gauge measures pressure where?

Answer 14

In the inlet manifold which relates to the engine power

Question 15

The fuel flow gauge measures what?

Answer 15

The amount of fuel delivered by the fuel system which relates to the engine power

Question 16

What is the tachometer used to monitor?

Answer 16

Engine power and to ensure the engine is operated within certified limits

Question 17

What air/fuel mixture burns the slowest?

Answer 17

Lean

Question 18

Some aircraft use ________ ignition timing.

Answer 18

Staggered

Question 19

What does a float carburetor do?

Answer 19

Provides a uniform air/fuel mixture as the airflow varies
Has an internal reservoir for fuel that maintains a constant level with a float/valve mechanism

Question 20

What does the Venturi do?

Answer 20

Converts potential energy to kinetic energy or pressure to velocity
-Proportions the fuel/air mixture
-Decreases the pressure at the discharge nozzle
-Limits the airflow at full throttle

Question 21

Where does the fuel level inside of a float bowl need to be adjusted to?

Answer 21

Slightly below the discharge nozzle outlet

Question 22

Where is the discharge nozzle located?

Answer 22

In the Venturi

Question 23

What is Air Bleed?

Answer 23

Aids in atomizing by increasing surface area of fuel.
Keeps a constant air/fuel ratio as air flow varies

Question 24

What does the Metering Jet do?

Answer 24

Restricts maximum amount of fuel

Question 25

What are the two types of mixture control?

Answer 25

Variable orifice & Back suction

Question 26

How does a variable orifice work?

Answer 26

Restricts fuel leaving float bowl

Question 27

How does back suction work?

Answer 27

Reduces float chamber pressure reducing fuel metering force

Question 28

What is an economizer?

Answer 28

Power Enrichment System Adds additional fuel at high power settings for cooling purposes

Question 29

What is the purpose of the acceleration system?

Answer 29

Allows fuel to be fed from nozzle until flow can be generated (Because fuel lags behind the airflow)

Question 30

Can an A&P overhaul a pressure carburetor?

Answer 30

No, it is considered a major repair

Question 31

What is the function of Chamber A in a pressure carb?

Answer 31

Impacts air pressure

Question 32

What is the function of Chamber B in a pressure carb?

Answer 32

Venturi Pressure

Question 33

What is the function of Chamber C in a pressure carb?

Answer 33

Metered fuel

Question 34

What is the function of Chamber D in a pressure carb?

Answer 34

Unmetered fuel

Question 35

What keeps a constant pressure inside of a pressure carburetor?

Answer 35

The discharge nozzle needle valve