Carburetion. Ch 8. Explain theory of operation of a basic carburetor.. I.D. and understand the function of all carburetor parts. . Understand the effect of atmospheric pressure on the fuel system of a small gas engine.. ID: 460519
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Presentations text content in Small Engine
Slide1
Small EngineCarburetion
Ch 8
Explain theory of operation of a basic carburetor.I.D. and understand the function of all carburetor parts. Understand the effect of atmospheric pressure on the fuel system of a small gas engine.Identify 3 basic types of carburetors.
Chapter Objectives - Upon completion of this chapter you should be able to:
Revised 10/01
Slide2
Principles of Carburetion
The amount of air needed for combustion is far greater than the amount of fuel. One pound of air would take up a much greater space than one pound of fuel.Air-fuel by volume:One cubic foot of gas would have to be mixed with 9000 cu ft of air to be at a 15 to 1 weight ratio
Ch 8
Slide3
Principles of Carburetion
Primary purpose is to produce a mixture of fuel and air to operate an engine.Engines cannot run on “liquid” gasoline.Must be able to maintain air/fuel mixtureCold or hot startingIdlingPartial throttleAccelerationHigh Speed operation
Ch 8
Slide4
Principles of Carburetion
Ch 8
Air-fuel
mixture
1) 14.7-1 Ratio (
15 parts
air
to 1 part
fuel
Slide5
Carburetor Pressure Differences
A carburetor is a device that ……Vacuum- Any pressure less than atmospheric pressureAtmospheric Pressure- the pressure produced by the weight of air molecules above the earth. 1. 29.92 Hg
Ch 8
Slide6
Carburetor Pressure Differences
Ch 8
Elevation and its effect on Atmospheric Pressure
Hg-Mercury
Slide7
Carburetor Pressure Differences
Venturi PrincipleA restriction in a passage, which causes air to move faster. Pressure in the passageway is reduced3. Vacuum created by the decreased pressure which allows fuel to be drawn into the airstream
Ch 8
Slide8
Small EngineCarburetion
Ch 8
Venturi Principle
Slide9
Types of Carburetors
A. Natural Draft Carburetor 1. Used when there is little space on top of the engine 2. Air flows horizontally into the manifold
Ch 8
Slide10
Types of Carburetors
B. Updraft Carburetor
Ch 8
Placed low on the engine and uses gravity fed fuel supply
Air-fuel mixture must be forced upward
Slide11
Types of Carburetors
C. Downdraft Carburetor
Ch 8
Operates with lower air velocities and larger passages
Air-fuel must flow downward
Slide12
Small EngineCarburetion
Ch 8
Carburetor Draft Types
Slide13
Float-type Carburetors
Float SystemFloat-a small sealed vessel made of brass or plasticThe purpose of the float is to maintain a constant level of fuel in the float bowl3. As the fuel is used in the float bowl, a needle valve is unseated to allow more fuel in the bowl. As the float rises, the needle valve seals the line to shut off the fuel.
Ch 8
Slide14
Float-type Carburetors
B. Choke System 1. The choke is a round disc mounted at the intake end of the carburetor 2. When closed, the choke cuts off air to allow a richer (higher fuel to air ratio 7-1), air-fuel mixture,….
Ch 8
Slide15
Float-type Carburetors
Throttle System 1. The throttle is a round disc mounted beyond the main fuel nozzle 2. The purpose of the throttle is to regulate the amount of air-fuel mixture entering the cylinder(s). 3. Allows operator to vary engine speed
Ch 8
Slide16
Float-type Carburetors
D. Load Adjustment 1. Regulates the amount of fuel entering the main discharge nozzle a. Load adjust needle b. Fixed jet or orifice (non- adjustable
Ch 8
Slide17
Ch 8
Small Engine
Carburetion
Slide18
Float-type Carburetors
Acceleration System 1. On some systems, when the throttle is opened quickly, a large amount of air passes through the carburetor. A pump is used to force fuel into the carburetor to allow proper air/fuel mixture and maintain running engine.
Ch 8
Slide19
Float-type Carburetors
Acceleration System 2. Acceleration Well is a reservoir of fuel, during idle fuel rises inside nozzle and flows into acceleration well. When throttle valve is opened quickly fuel rushes through the holes in nozzle. This provides a richer mixture under sudden need for power.
Ch 8
Slide20Slide21
Float-type Carburetors
Economizer Circuit 1. Designed to retard fuel to the engine during part throttle, by lower pressure in float bowl
Ch 8
Slide22
Float-type Carburetors
G. Idling Circuit 1. Throttle valve is closed 2. Fuel transported through an idle circuit pathwayThrottle valve closed-idle system supplies just enough air-fuel to keep engine running
Ch 8
Slide23
Float-type Carburetors
Part-Throttle, Full Throttle Sequence 1. Other circuits outside of idling speed that have secondary discharge holes opened for more air/fuel mixture to open.
Ch 8
Slide24
Float-type Carburetors
G. Primer 1. Hand operated plunger 2. Forces addition fuel up the nozzle and/or pumps air pressure onto the float bowl which forces fuel into nozzle
Ch 8
Slide25
Ch 8
Slide26
Diaphragm-type Carburetors
Does not contain a float systemAtmospheric pressure and the vacuum created in the engine pulsates a flexible diaphragmThe diaphragm draws fuel into the chamber of the carburetor from which it is readily drawn into the venture
Ch 8
Slide27
Ch 8
Slide28
Negative pressure pulses from crankcase
Fuel pushed to carburetor
Fuel pulled from tank
Slide29Slide30Slide31Slide32
Small EngineCarburetion
Ch 8
Carburetion Fuel Systems
Suction Type
B&S = (Vacu-jet)
Pump TypeB&S = (Pulsa-jet)
Gravity Feed TypeB&S = (Flo-jet)
Slide33
Small EngineCarburetion
Ch 8
Carburetor Components and Operation
Slide34
Small EngineCarburetion
Ch 8
Old style carburetor
with an adjustable needle valve
Newer style carburetor
with a fixed Jet
(Jet must be replaced to for altitude adjustment)
Slide35
Small EngineCarburetion
Ch 8
When performing an altitude adjustment the jet is removed and replaced with a jet that has a smaller orifice.
Slide36
Small EngineCarburetion
Ch 8
Main Jet Location
Slide37
Small Engine
Carburetion
Ch 8
Main Jet Location
Slide38
Small Engine
Carburetion
Ch 8
Main Jet Location
Slide39
Small Engine
Carburetion
Ch 8
Main Jet Location
Slide40
A
A
B
C
D
Slide41
Ch 8
Small Engine
Carburetion
What other components are related to carburetion???
Download this presentation
DownloadNote - The PPT/PDF document "Small Engine" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Presentations text content in Small Engine
Small EngineCarburetion
Ch 8
Explain theory of operation of a basic carburetor.I.D. and understand the function of all carburetor parts. Understand the effect of atmospheric pressure on the fuel system of a small gas engine.Identify 3 basic types of carburetors.
Chapter Objectives - Upon completion of this chapter you should be able to:
Revised 10/01
Slide2Principles of Carburetion
The amount of air needed for combustion is far greater than the amount of fuel. One pound of air would take up a much greater space than one pound of fuel.Air-fuel by volume:One cubic foot of gas would have to be mixed with 9000 cu ft of air to be at a 15 to 1 weight ratio
Ch 8
Slide3Principles of Carburetion
Primary purpose is to produce a mixture of fuel and air to operate an engine.Engines cannot run on “liquid” gasoline.Must be able to maintain air/fuel mixtureCold or hot startingIdlingPartial throttleAccelerationHigh Speed operation
Ch 8
Slide4Principles of Carburetion
Ch 8
Air-fuel
mixture
1) 14.7-1 Ratio (
15 parts
air
to 1 part
fuel
Slide5Carburetor Pressure Differences
A carburetor is a device that ……Vacuum- Any pressure less than atmospheric pressureAtmospheric Pressure- the pressure produced by the weight of air molecules above the earth. 1. 29.92 Hg
Ch 8
Slide6Carburetor Pressure Differences
Ch 8
Elevation and its effect on Atmospheric Pressure
Hg-Mercury
Slide7Carburetor Pressure Differences
Venturi PrincipleA restriction in a passage, which causes air to move faster. Pressure in the passageway is reduced3. Vacuum created by the decreased pressure which allows fuel to be drawn into the airstream
Ch 8
Slide8Small EngineCarburetion
Ch 8
Venturi Principle
Slide9Types of Carburetors
A. Natural Draft Carburetor 1. Used when there is little space on top of the engine 2. Air flows horizontally into the manifold
Ch 8
Slide10Types of Carburetors
B. Updraft Carburetor
Ch 8
Placed low on the engine and uses gravity fed fuel supply
Air-fuel mixture must be forced upward
Slide11Types of Carburetors
C. Downdraft Carburetor
Ch 8
Operates with lower air velocities and larger passages
Air-fuel must flow downward
Slide12Small EngineCarburetion
Ch 8
Carburetor Draft Types
Slide13Float-type Carburetors
Float SystemFloat-a small sealed vessel made of brass or plasticThe purpose of the float is to maintain a constant level of fuel in the float bowl3. As the fuel is used in the float bowl, a needle valve is unseated to allow more fuel in the bowl. As the float rises, the needle valve seals the line to shut off the fuel.
Ch 8
Slide14Float-type Carburetors
B. Choke System 1. The choke is a round disc mounted at the intake end of the carburetor 2. When closed, the choke cuts off air to allow a richer (higher fuel to air ratio 7-1), air-fuel mixture,….
Ch 8
Slide15Float-type Carburetors
Throttle System 1. The throttle is a round disc mounted beyond the main fuel nozzle 2. The purpose of the throttle is to regulate the amount of air-fuel mixture entering the cylinder(s). 3. Allows operator to vary engine speed
Ch 8
Slide16Float-type Carburetors
D. Load Adjustment 1. Regulates the amount of fuel entering the main discharge nozzle a. Load adjust needle b. Fixed jet or orifice (non- adjustable
Ch 8
Slide17Ch 8
Small Engine
Carburetion
Slide18Float-type Carburetors
Acceleration System 1. On some systems, when the throttle is opened quickly, a large amount of air passes through the carburetor. A pump is used to force fuel into the carburetor to allow proper air/fuel mixture and maintain running engine.
Ch 8
Slide19Float-type Carburetors
Acceleration System 2. Acceleration Well is a reservoir of fuel, during idle fuel rises inside nozzle and flows into acceleration well. When throttle valve is opened quickly fuel rushes through the holes in nozzle. This provides a richer mixture under sudden need for power.
Ch 8
Slide20Slide21Float-type Carburetors
Economizer Circuit 1. Designed to retard fuel to the engine during part throttle, by lower pressure in float bowl
Ch 8
Slide22Float-type Carburetors
G. Idling Circuit 1. Throttle valve is closed 2. Fuel transported through an idle circuit pathwayThrottle valve closed-idle system supplies just enough air-fuel to keep engine running
Ch 8
Slide23Float-type Carburetors
Part-Throttle, Full Throttle Sequence 1. Other circuits outside of idling speed that have secondary discharge holes opened for more air/fuel mixture to open.
Ch 8
Slide24Float-type Carburetors
G. Primer 1. Hand operated plunger 2. Forces addition fuel up the nozzle and/or pumps air pressure onto the float bowl which forces fuel into nozzle
Ch 8
Slide25Ch 8
Slide26Diaphragm-type Carburetors
Does not contain a float systemAtmospheric pressure and the vacuum created in the engine pulsates a flexible diaphragmThe diaphragm draws fuel into the chamber of the carburetor from which it is readily drawn into the venture
Ch 8
Slide27Ch 8
Slide28Negative pressure pulses from crankcase
Fuel pushed to carburetor
Fuel pulled from tank
Slide29Slide30Slide31Slide32Small EngineCarburetion
Ch 8
Carburetion Fuel Systems
Suction Type
B&S = (Vacu-jet)
Pump TypeB&S = (Pulsa-jet)
Gravity Feed TypeB&S = (Flo-jet)
Slide33Small EngineCarburetion
Ch 8
Carburetor Components and Operation
Slide34Small EngineCarburetion
Ch 8
Old style carburetor
with an adjustable needle valve
Newer style carburetor
with a fixed Jet
(Jet must be replaced to for altitude adjustment)
Slide35Small EngineCarburetion
Ch 8
When performing an altitude adjustment the jet is removed and replaced with a jet that has a smaller orifice.
Slide36Small EngineCarburetion
Ch 8
Main Jet Location
Slide37Small Engine
Carburetion
Ch 8
Main Jet Location
Slide38Small Engine
Carburetion
Ch 8
Main Jet Location
Slide39Small Engine
Carburetion
Ch 8
Main Jet Location
Slide40A
A
B
C
D
Slide41Ch 8
Small Engine
Carburetion
What other components are related to carburetion???
Slide42Ch 8
Determine proper Air Fuel Ratio under load
by sparkplug coloration
Small EngineCarburetion
Slide43Slide44Small EngineCarburetor
Ch 8
Pneumatic Governor
Slide45Small EngineCarburetion
Ch 8
Mechanical Governor
Slide46Mechanical Governor Operation
Slide47Mechanical Governor Operation
Slide48Mechanical Governor Operation
Slide49Small EngineCarburetion
Ch 8
Air Cleaner
Dry Element
Slide50Slide51Slide52Slide53Slide54Slide55Slide56Slide57Slide58Slide59