12.12.6(f) . idle cut-off. 

A valve in the carburetor which closes the fuel off between the float chamber and the venturi. Used to shut down the motor because it ensures that all fuel in the manifold is burned before the motor stops

12.12.6(e) . mixture control; 

Function – regulating the amount of fuel being metered into the air at any given throttle setting

Operational use of mixture control
– FULL RICH for take-off unless at very high elevation airfield
– left in FULL RICH for the climb ( unless climbing to a high altitude)
– place on FULL RICH at the top of a descent (unless descending from a high altidude in which case it would be progressively enriched until full rich at lower altitude)
-Idle cut-off is normal means of shutting the engine down
–

12.12.6(d) . enrichment at high power settings; 

Enrichment system
– provides extra fuel when the throttle apporaches and reaches its wide open position
-his excess fuel does not burn but provides cooling through evaporation at high power settings
– helps to prevent overheating and detonation

12.12.6(c) . acceleration enrichment; 

Is used to ensure that sufficient fuel is available when a sudden opening of the throttle causes a rapid increase in airflow through the carburettor

12.12.6(b) . idling circuit; 

Aircraft carburetors will normally have an idling circuit to provide fuel to the engine when the butterfly is closed and the main fuel jet delivery becomes less reliable.

12.12.6(a) . atomisation and diffusion; 

Atomisation and Diffusion
-In order for the fuel to mix properly with the air in the intake manifold it needs to be atomised and diffused among the air. To assist with this an atomisation and diffusion unit is positioned at the main jet outlet to improve the vapourisation of the fuel.

12.12.6. State the function and/or purpose of the following within the carburettor:

12.12.4. Explain the basic principle of operation of a simple float-type carburettor.

Diagram

12.12.2. Explain the principle of carburation.

The device used to mix the fuel with the air is called the Carburettor
– the main fuel outlet of the carburettor is in the low pressure area at the centre of a venturi
– when air flows through the venturi the lowered pressure results in fuel being drawn or sucked from the jet
– the jet is calibrated so that it meters or delivers the required proportion of fuel into the air before the mixture enters the engine
– after it leaves the main jet, the fuel vaporises and and mixes with the air on its passage past the throttle butterfly and trhough the inlet manifold to the cylinders

12.10.6. Explain the basic principle of operation of a four stroke internal combustionengine. 

The four stroke engine operates on what is known as the Otto Cycle.
1. Intake – inlet valve open
2. Compression – both valves closed
3. Power – both valves closed – mixture ignited
4. Exhaust – exhaust valve open
(Diagram)