Carburettors/Carby Heat Flashcards
Carburettors:
Total Pressure = ______ + ______
Total Pressure = Static pressure + Dynamic pressure
What is a float chamber?
What does it do?
- Vented reservoir
- Holds fuel from the tank using a float & amp valve
What is a venturi ?
- Narrowing section
- Creates a suction
List the pros of carburettors
- Simple (no moving parts)
- Cheap
- Reliable
- Efficient for small engines
- Mixture control –> controls fuel into main jet
List the cons of carburettors
- Prone to carburettor icing
- unable to operate in __ altitudes
- Unable to deliver same amount of fuel to each cylinder
- Inefficient in high performance
What does the accelerator pump do?
- Sends surge of fuel –> discharge nozzel as throttle opened rapidly to overcome power lag
What is impact ice?
- Water turns to ice on impact
- Components are below 0 degrees C
Fuel evaporation:
- What does it cause?
- What is is caused by?
Causes:
- Throttle ice inside carburettor
- Increased when throttle partly open/closed
Caused by:
- Temp drop of ____ fuel (adiabatic cooling)
- 3-4 degree drop in temp
What are the symptoms of carby ice?
- Drop in manifold pressure
- Rough running
- Back firing
What are the conditions most likely to cause carby ice?
What combination of temp and humidity = serious risk?
- < 20 degrees C
- 80% humidity
- Decent = low power settings
- Clouds (closer = more risk)
Serious risk = 10 degreesC & 70-80% humidity
Describe carby heat
- Hot air = less dense –> mixture becomes richer
- test should drop rmp when open
- can supply alternate air supply in emergency
Fuel injection systems: PROS
- not gravity sensitive = operate in unusual altitudes
- allows more precise over mixture strength @ each cylinder
- Free from icing
Fuel injection systems: CONS
- More complex
- More expensive
- Many fuel lines = prone to air locks
- Fuel pump driven by engine gear
Fuel air control unit - what does it do?
- senses amount air flowing to engine
- metres & sends amount fuel to manifold valve (gear driven)
Fuel manifold valve:
Where situated
What does
- Situation top of engine
- Distributes metered fuel to discharge nozzles