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27 Cards in this Set
- Front
- Back
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What is the Stoichiometric (Chemically Correct) mixture ratio?
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15:1
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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?
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15%
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What is the Power Enrichment/Economiser System for?
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Enrichening the mixture when full power is being used to allow extra cooling due to the excess of fuel.
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What is the Throttle Butterfly's job?
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To control the weight of charge allowed into the engine.
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What is the Diffusers Job?
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Atomising the fuel.
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What are the six carburettor systems?
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Main Metering System,
Idling System, Power Enrichment/Economiser, Mixture Control unit, Idle Cut Off, Accelerating System. |
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What does the Main Metering System do?
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Supplies the correct amount of fuel to the engine at all speeds above idling. All carburettors have a main metering jet.
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What does the idling system do?
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Allows extra fuel to flow through when airflow through the venturi is minimal causing the main meteing jet to not function.
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What does the accelerating system do?
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Supplies extra fuiel during a sudden increase in engine power. (This is a one off mechanism)
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What does the Power Enrichment/Economiser system do?
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Automatically increases the richness of mixture during high power operation by supplying extra fuel for cooling and suppression of detonation.
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What does the mixture control system do?
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Leans the mixture either manually or automatically.
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What does the idle cut off system do?
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Pressure differential in the float chamber is reduced to zero stopping kick back, induction fires and leaving an ignitable charge in the cylinder.
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What are the four disadvantages of float chambers?
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Prone to venturi icing,
Friction, Cut out when inverted, Float jamming up due to turbulence. |
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What is Impact Icing?
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Supercooled water that turns to ice on contact with an air intake below 0°.
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What is Adiabatic Icing?
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(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. |
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What is Refrigeration Icing?
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(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. |
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What are the four symptoms of Icing?
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Decrease in RPM
Decrease in Manifold Pressure Decrease in IAS Decrease in Altitude |
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How do you cure adiabatic and refrigeration icing?
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Apply Carb Heat (alternative air system).
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What is the main advantage of Pressure Carburettors?
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They avoid Icing.
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What are six advantages of pressure carburettors?
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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. |
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What is fuel injection?
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When fuel is injected directly into the cylinder or intake manifold leaving only air in the induction system.
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What are the two main fuel injection systems?
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Low Pressure - Continuous flow
High Pressure - Direct Injection |
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What are six advantages of fuel injection?
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No Refrigeration Icing,
Uniform mixture to each cylinder, Inproved ratio control, Reduced Maintenance, Quick acceleration response, Increased engine efficiency. |
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What are four disadvantages of fuel injection?
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Vapour Locks,
Need electric boost pump, Susceptibility to contamination, Need awareness of fuel distribution. |
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Why Lean? (8 Reasons)
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Improved engine efficiency,
Greater fuel economy, Greater endurance, smoother engine operation, Longer spark plug life, Reduced maintenance costs, Reduced operating costs, desirable engine temperatures. |
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When to Lean?
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Anytime the engine is at 75% power or less at any altitude.
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What are the four methods of leaning?
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Tachometer Method,
Engine "Rough" Method, Fuel Flow Method, Exhaust Gas Temperature Method |
