1. Carburetors and Exhaust Systems4 7 . 3
Carburetors and Exhaust Systems

2. The Carburetor The carburetor has three important functions:
measure the correct quantity of fuel and vaporize this fuel,
mix it with air in the proper proportion, and
deliver the mixture to the cylinders.
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3. Components of a Carburetor
Venturi
air is drawn into the venturi and because of its shape, the air is accelerated while the pressure is reduced
Nozzle
provides a passage for fuel from the float chamber to the venturi
reduced pressure draws fuel into the venturi where it is vaporized
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4. Components of a Carburetor
Throttle Valve
regulates the volume of fuel/air mixture
Intake Manifold
distributes the fuel/air mixture from the carburetor to the cylinders
Float Chamber
contains a consistent level of fuel in order to keep fuel supply steady
Throttle Valve To
Intake
Manifold
Float
Chamber
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5. Components of a Carburetor
Needle Valve
opens and closes the fuel line and is controlled by the float
Vent
allows the pressure to be equalized with that of the changing outside air pressure
Idle Jet
used to keep the engine going when there is insufficient air flow to draw in fuel from the nozzle
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6. Fuel/Air Mixture
The ratio of fuel to air is regulated by the pilot with the mixture control.
The throttle valve regulates the flow of air/fuel mixture into the engine. It also creates turbulence to assist in the mixing of fuel and air.
The proportion of fuel to air is governed by weight and not by volume.
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7. Fuel/Air Mixture
The chemically correct mixture is about 1:15, where it is one part fuel to fifteen parts air.
An engine will run hotter with a lean mixture because the lean mixture is slower burning, exposing the cylinder walls to high temperatures for a longer period of time.
An engine will run cooler with a richer mixture because the rich mixture burns more quickly.
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8. NOTE: You must use the buttons in the Confirmation Stage
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9. Aero Engines Carburetor and Exhaust Systems
Let's try a few review questions on Aero Engines:
Question #1 - How is the mixture of gasoline to air measured?
Volume A B
Weight C
Mass D
Area
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14. Mixture Control As altitude increases, the density of air decreases.
Carburetors are calibrated for sea level operation.
Therefore, with altitude, the mixture would become over-rich, causing a waste of fuel and a loss of power.
Mixture control is fitted to adjust the amount of fuel being drawn from the nozzle.
Mixture control can be used to produce a rich or lean fuel/air mixture.
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15. Rich Mixture
Besides lowering the combustion temperature, too rich a mixture will result in unburned wasted fuel.
It contributes to fouled spark plugs and combustion chamber deposits.
Can also cause rough engine operation, appreciable loss of power or engine failure.
Used for high power settings.
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16. Lean Mixture
May cause rough engine operation, sudden “cutting out”, “popping back” or back-firing, detonation, overheating or appreciable loss of power.
Continual operation at too lean a mixture has also been responsible for engine failure.
Used for cruise power settings.
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17. When to Lean the Engine
At cruise power, below approximately 75% of the rated RPM of the engine.
At any altitude above 3000 feet.
For take-off at high altitude airports.
After climbing to a higher altitude.
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18. Why Lean the Engine
Proper leaning of engine is both practical and economical. It results in:
economy of fuel,
a smoother running engine,
a more efficient engine,
extended range,
less spark plug fouling,
more desirable engine temperatures, and
cleaner combustion chambers.
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19. NOTE: You must use the buttons in the Confirmation Stage

20. Aero Engines Carburetor and Exhaust Systems
Let's try a few review questions on Aero Engines:
Question #2 - When do you lean your engine?
Take off at low altitude A
Final approach B
Climbing at high altitudes C
Climbing at low altitudes D
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25. Aero Engines Carburetor and Exhaust Systems
Let's try a few review questions on Aero Engines:
Question #3 - Why do you lean your engine?
Extended range A
Longer spark plug life B
Cleaner engine C
All the above D
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30. Carburetor Icing
Forms under moist atmospheric conditions with air temperatures anywhere from approximately -5C to 30C.
Indicated by a loss of power (RPM drop).
Can cause complete engine failure.
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31. Forms of Carburetor Ice
There are three forms of carburetor ice:
fuel vaporization ice,
impact ice, and
throttle ice.
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32. Prevention of Carb Icing
Carb icing does not occur in engines that have fuel injectors rather than a carburetor.
Carb heat uses air heated by the exhaust system which is pumped into the carburetor.
Results in initial drop in RPM.
If ice is present, its melting will give a short period of engine roughness.
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33. Exhaust System Basically a scavenging system.
Collects and disposes of the high temperature, noxious gases discharged by the engine.
Main function is to prevent the escape of these potentially destructive gases into the airframe and cabin.
Two types:
short stack system, and
collector system.
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34. Short Stack Exhaust System
Used on non-turbocharged engines and on low powered engines.
Relatively simple:
a down stack from each cylinder,
an exhaust collector tube on each side of the engine, and
an exhaust ejector on each side of the cowling.
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35. Collector Exhaust System
Used on most large engines and on all turbocharged engines.
Individual exhaust headers empty into a collector ring that collects the exhaust from all the cylinders.
One outlet from this rings routes the hot exhaust gas to the turbocharger.
An exhaust tailpipe carries the gases away.
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36. NOTE: You must use the buttons in the Confirmation Stage
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37. Aero Engines Carburetor and Exhaust Systems
Let's try a few review questions on Aero Engines:
Question #4 - At approximately what temperature range can carburetor ice form?
-5°C to 30°C A B
-30°C to -5°C C
-30°C to 5°C D
5°C to 30°C
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42. Aero Engines Carburetor and Exhaust Systems
Let's try a few review questions on Aero Engines:
Question #5 - Which is NOT a type of exhaust system?
Short Stack A
Collector B
Venturi C
Both B and C D
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47. Aero Engines Carburetor and Exhaust Systems Congratulations!!
You have now completed the Carburetor and Exhaust Systems lesson of the Aero Engines Module. Of course, this lesson is always available to you for future reference if required.
You are now ready to move along to the next Aero Engines lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam.
Good Luck!
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