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27 Cards in this Set

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  • Back
What is the Stoichiometric (Chemically Correct) mixture ratio?
In Practice how much is the mixture ratio en-richened by from the chemically correct ratio to ensure the leanest cylinder recieves an adequate mixture?
What is the Power Enrichment/Economiser System for?
Enrichening the mixture when full power is being used to allow extra cooling due to the excess of fuel.
What is the Throttle Butterfly's job?
To control the weight of charge allowed into the engine.
What is the Diffusers Job?
Atomising the fuel.
What are the six carburettor systems?
Main Metering System,
Idling System,
Power Enrichment/Economiser,
Mixture Control unit,
Idle Cut Off,
Accelerating System.
What does the Main Metering System do?
Supplies the correct amount of fuel to the engine at all speeds above idling. All carburettors have a main metering jet.
What does the idling system do?
Allows extra fuel to flow through when airflow through the venturi is minimal causing the main meteing jet to not function.
What does the accelerating system do?
Supplies extra fuiel during a sudden increase in engine power. (This is a one off mechanism)
What does the Power Enrichment/Economiser system do?
Automatically increases the richness of mixture during high power operation by supplying extra fuel for cooling and suppression of detonation.
What does the mixture control system do?
Leans the mixture either manually or automatically.
What does the idle cut off system do?
Pressure differential in the float chamber is reduced to zero stopping kick back, induction fires and leaving an ignitable charge in the cylinder.
What are the four disadvantages of float chambers?
Prone to venturi icing,
Cut out when inverted,
Float jamming up due to turbulence.
What is Impact Icing?
Supercooled water that turns to ice on contact with an air intake below 0°.
What is Adiabatic Icing?
(Throttle Butterfly Icing)
When there is a change in pressure causing a change in temperature around the throttle butterfly. Small throttle butterfly openings are a main cause.
What is Refrigeration Icing?
(Fuel Icing)
When the fuel changes from a liquid to a vapour latent heat is absorbed causing icing.
High relative humidity is one of the main causes.
It can occur at +32°C.
What are the four symptoms of Icing?
Decrease in RPM
Decrease in Manifold Pressure
Decrease in IAS
Decrease in Altitude
How do you cure adiabatic and refrigeration icing?
Apply Carb Heat (alternative air system).
What is the main advantage of Pressure Carburettors?
They avoid Icing.
What are six advantages of pressure carburettors?
Resistant to Icing
Gravity & Inertia have little effect
Accurate Fuel Metering for all throttle / altitude settings
Protection against fuel boiling / vapour lock
Improved Atomisation
No fuel lag on acceleration.
What is fuel injection?
When fuel is injected directly into the cylinder or intake manifold leaving only air in the induction system.
What are the two main fuel injection systems?
Low Pressure - Continuous flow
High Pressure - Direct Injection
What are six advantages of fuel injection?
No Refrigeration Icing,
Uniform mixture to each cylinder,
Inproved ratio control,
Reduced Maintenance,
Quick acceleration response,
Increased engine efficiency.
What are four disadvantages of fuel injection?
Vapour Locks,
Need electric boost pump,
Susceptibility to contamination,
Need awareness of fuel distribution.
Why Lean? (8 Reasons)
Improved engine efficiency,
Greater fuel economy,
Greater endurance,
smoother engine operation,
Longer spark plug life,
Reduced maintenance costs,
Reduced operating costs,
desirable engine temperatures.
When to Lean?
Anytime the engine is at 75% power or less at any altitude.
What are the four methods of leaning?
Tachometer Method,
Engine "Rough" Method,
Fuel Flow Method,
Exhaust Gas Temperature Method