Carburettor

Question 1

What component controls airflow in a carburettor?

Answer 1

Butterfly

Question 2

What is the air pressure like in a carburettor’s float chamber?

Answer 2

It is atmospheric

Question 3

Where is atmospheric pressure found in a carburettor?

Answer 3

Float chamber

Question 4

How is fuel made to flow into the venturi airflow?

Answer 4

High pressure in float chamber and lower pressure in venturi

Question 5

What factor influences the mass of fuel flowing in a carburettor?

Answer 5

Speed of airflow in venturi

Question 6

Faster airflow in a carburettor venturi means what is also greater?

Answer 6

Differential pressure between flloat chamber and venturi
And thus the greater the fuel flow

Question 7

How is fuel flow increased in a carburettor?

Answer 7

Differential pressure increases causes more fuel to flow into the venturi

Question 8

What happens to fuel/air ratio when throttle is set to maximum power?

Answer 8

Airflow increases at a greater rate than fuel flow

Question 9

What is used to overcome airflow increasing at greater rate than fuel flow when throttle is fully open?

Answer 9

Accelerator pump

Question 10

What component allows engine to run smoothly at idle power?

Answer 10

Idling jet

Question 11

When an engine is idling, what happens to differential pressure in a carburettor?

Answer 11

It is insufficient to force fuel into the venturi chamber

Question 12

When a carburettor’s differential pressure is insufficient to prompt fuel flow, what can be said about the engine?

Answer 12

It is idling

Question 13

What are the two types of mixture control in a carburettor?

Answer 13

Needle and back suction

Question 14

Why is it good practice to have Mixture fully rich in a climb?

Answer 14

The excess fuel helps cool the engine

Question 15

What does excess fuel do with regards to engine operation?

Answer 15

Acts as a cooling agent

Question 16

What assists in engine cooling in a climb in relation to the carburettor?

Answer 16

Excess fuel when Mixture is fully rich

Question 17

What carburettor setting will result in higher CHT?

Answer 17

Lean mixture

Question 18

Over-rich mixture symptoms

Answer 18

Loss of power
High fuel consumption
Spark plug fouling

Question 19

What is the major outcome of an excessively lean mixture setting?

Answer 19

Detonation

Question 20

Why is use of idle cut-off a safe way of shutting down an engine?

Answer 20

No combustible fuel/air mixture is left in the carburettor

Question 21

Detonation is likely with what power setting?

Answer 21

Excessively lean mixture

Question 22

Why is detonation an outcome of an excessively lean mixture?

Answer 22

Excessively lean means very high cylinder head temperatures

Question 23

What happens if pressure and temp rise in a cylinder is too high?

Answer 23

Detonation

Question 24

What happens to temperature of a gas when it is compressed?

Answer 24

It rises

Question 25

What items should be performed if detonation has occured?

Answer 25

Enrichen the mixture Reduce cylinder pressure (throttle back) Increase airspeed to assist cooling

Question 26

In pre-ignition, when does combustion occur?

Answer 26

Before the spark plug operates

Question 27

Difference between detonation and pre-ignition combustion

Answer 27

Detonation is explosive combustion, pre-ignition is progressive

Question 28

Difference between detonation and pre-ignition in engine conditions

Answer 28

Detonation applies to whole engine, pre-ignition is unique to one cylinder

Question 29

What often causes pre-ignition?

Answer 29

Carbon deposit in a cylinder

Question 30

What happens to temperature as air accelerates through a carburettor venturi?

Answer 30

It drops

Question 31

What kind of ice occurs in a carburettor if super-cooled water droplets come into contact with the carburettor's components?

Answer 31

Impact ice

Question 32

How can impact ice form in a carburettor in moist, warm temperatures?

Answer 32

The carburettor's components are sub-zero from higher altitudes

Question 33

When fuel vaporises, what happens to its temperature?

Answer 33

It falls substantially

Question 34

Why does temperature fall substantially when fuel vaporises?

Answer 34

It absorbs latent heat

Question 35

The absorption of latent heat by fuel in vaporisation has what effect?

Answer 35

Substantial temperature reduction

Question 36

How does fuel ice form?

Answer 36

Fuel vaporisation reduces air temperature to below 0 degrees Moisture in fuel/air mixture precipitates and forms ice

Question 37

Why does temperature decrease after air/fuel passes the butterfly (throttle valve)?

Answer 37

Static pressure decreases, thus reducing temperature

Question 38

When is the acceleration and temperature drop of fuel/air greatest in a carburettor?

Answer 38

At low throttle settings

Question 39

Why is the acceleration and temperature drop of fuel/air greatest at low throttle settings?

Answer 39

Butterfly restricts airflow the most at these settings, creating greater pressure drops

Question 40

When does a butterfly's pressure changes occur most drastically?

Answer 40

At lower throttle settings because airflow is restricted the most

Question 41

Visible moisture is not necessary for what kind of carburettor icing?

Answer 41

Throttle ice

Question 42

What is throttle ice?

Answer 42

Fuel/air mixture accelerates, pressure drops and temeprature drops Ice forms on throttle valve

Question 43

3 types of carburettor icing?

Answer 43

Impact ice Fuel ice Throttle ice

Question 44

What types of carburettor icing occurs with high OATs?

Answer 44

Fuel and throttle ice

Question 45

Carb heat appplication involves an initial reduction of engine power how?

Answer 45

Heated air is less dense

Question 46

What replaces carb heat in a fuel-injection system?

Answer 46

Alternate air

Question 47

In a fuel-injection system, why is a venturi still present?

Answer 47

It senses the pressure differential

Question 48

Approximate fuel/air ratio for a rich mixture?

Answer 48

1:8

Question 49

Approximate fuel/air ratio for a lean mixture?

Answer 49

1:20