Carb. Fuel Injection

8/20/2019 Carb. Fuel Injection

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BY MELODIAS BEN HUR


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Functions of CarburetorsFunctions of Carburetors

• A Mixing ValveA Mixing Valve

• Mixes Fuel & AirMixes Fuel & Air

• Meters Fuel FlowMeters Fuel Flow

• Atomizes Fuel for UseAtomizes Fuel for Use

• Controls Air FlowControls Air Flow

– Engine SpeedEngine Speed


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Ways to Classify CarburetorsWays to Classify Carburetors

• Size: (2)Size: (2)

• Air Flow Direction: (3)Air Flow Direction: (3)

• Fuel Type: (4)Fuel Type: (4)

• Barrels: (3)Barrels: (3)

• General: (3)General: (3)

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Carburetor Parts & Their FunctionsCarburetor Parts & Their Functions

• In order to understandIn order to understand

how each part of ahow each part of a

carburetor works youcarburetor works youshould first build one.should first build one.

• Building a carburetor onBuilding a carburetor on

paper will allow you topaper will allow you tosee how each part workssee how each part works

and why it is needed.and why it is needed.


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Step #1: Air HornStep #1: Air Horn

• Simple RoundSimple Round

Metal TubeMetal Tube

• Flange Bolts toFlange Bolts to

Intake ManifoldIntake Manifold

• Serves as an AirServes as an Air

Passage for AirPassage for Air

Entering the EngineEntering the Engine


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Step #2: Fuel BowlStep #2: Fuel Bowl

• Attached to Air HornAttached to Air Horn

• Holds a Supply ofHolds a Supply of

GasGas• Float Inside Bowl: (3)Float Inside Bowl: (3)

• Vent: (2)Vent: (2)


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Step #3: Main Discharge TubeStep #3: Main Discharge Tube

• Allows Fuel to beAllows Fuel to beTransfered from theTransfered from the

Fuel Bowl to theFuel Bowl to the

Air Horn.Air Horn.


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Step #4: The VenturiStep #4: The Venturi

• A vacuum is neededA vacuum is needed

to transport the fuel.to transport the fuel.

• The engine doesn’tThe engine doesn’tcreate enoughcreate enough

vacuum by itself.vacuum by itself.

• The Venturi increasesThe Venturi increasesair speed: (4)air speed: (4)


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Step #5: Secondary VenturiStep #5: Secondary Venturi

• Creates more vacuum.Creates more vacuum.

• Position: (2)Position: (2)

• Multiples the vacuum.Multiples the vacuum.

• ““Booster Venturi”Booster Venturi”

• Some carburetors haveSome carburetors have

a 3rd venturi.a 3rd venturi.


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Step #6: Air BleedStep #6: Air Bleed

• Reduces droplet sizeReduces droplet size• Introduces a stream of air into the fuel traveling upIntroduces a stream of air into the fuel traveling up

the main discharge tube.the main discharge tube.

• Smaller droplets carry into the engine properly.Smaller droplets carry into the engine properly.


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Step #7: JetsStep #7: Jets

• Introduction: (1)Introduction: (1)

• Purpose &Purpose &

Operation: (4)Operation: (4)


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Step #8: Choke ValveStep #8: Choke Valve

• Purpose: (2)Purpose: (2)

• Placement: (1)Placement: (1)

• Operation: (2)Operation: (2)


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Step #9: Throttle ValveStep #9: Throttle Valve

• The Engine Will NowThe Engine Will Now

Start!Start!

– How will it Run?How will it Run?• Throttle ButterflyThrottle Butterfly

Controls the Engine’sControls the Engine’s

Speed: (3)Speed: (3)


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CircuitsCircuits

• The carburetor is complete but it still farThe carburetor is complete but it still far

from perfect!from perfect!

• What are Circuits?What are Circuits?

• Types of Circuits: (7)Types of Circuits: (7)

• Purpose of Circuits: (1)Purpose of Circuits: (1)


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Engine Problems Kept on TrackEngine Problems Kept on Track

By Circuits:By Circuits:• Idle:Idle:

• Partial Throttle Operation:Partial Throttle Operation:

• High Speed Cruising:High Speed Cruising:

• High Speed Full Power:High Speed Full Power:

• Acceleration Hesitation:Acceleration Hesitation:• Rich Mixture for Cold Starting:Rich Mixture for Cold Starting:

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Small Engine CarburetorsSmall Engine Carburetors

• Types:Types:

– Float TypeFloat Type

– Suction TypeSuction Type

– Pulsating Suction Lift TypePulsating Suction Lift Type

– Diaphram TypeDiaphram Type


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Float Type CarburetorFloat Type Carburetor

• Now CommonNow Common

on Briggs &on Briggs &

Stratton EnginesStratton Engines

• Fuel Bowl &Fuel Bowl &

Float System: (6)Float System: (6)


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Suction Type Carburetor:Suction Type Carburetor: (Vacu-Jet)(Vacu-Jet)

• Common in olderCommon in older

Briggs & StrattonBriggs & Stratton

engines.engines.• Suction tubes pullSuction tubes pull

the fuel up.the fuel up.


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Pulsating Suction Lift Carburetor:Pulsating Suction Lift Carburetor:

(Pulsa-Jet)(Pulsa-Jet)– Briggs & Stratton Pulsa-JetBriggs & Stratton Pulsa-Jet

– Has a fuel pump built in: (1)Has a fuel pump built in: (1)

– Provides more Hp than a suction type: (2)Provides more Hp than a suction type: (2)

– Allows the air tube in the carb. to be larger b/cAllows the air tube in the carb. to be larger b/c

the fuel does not have to be lifted so far.the fuel does not have to be lifted so far.


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Diaphram CarburetorDiaphram Carburetor

– Has flexible diaphrams: (1)Has flexible diaphrams: (1)

– Allows function at any positionAllows function at any position

– Popular on 2-cycle enginesPopular on 2-cycle engines


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Despite all of it’s advances the carburetor is still a compromise of efficiency.Despite all of it’s advances the carburetor is still a compromise of efficiency.

The carburetor’s limitations have pushed the industry towards fuel injectionThe carburetor’s limitations have pushed the industry towards fuel injection.


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Fuel Injection ArrangementsFuel Injection Arrangements

•Direct Fuel Injection:Direct Fuel Injection:

• Throttle Body Fuel Injection:Throttle Body Fuel Injection:

• Multi-Point (Port) Fuel Injection:Multi-Point (Port) Fuel Injection:


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Direct Fuel InjectionDirect Fuel Injection

– Fuel injected directlyFuel injected directlyinto the combustioninto the combustion

chamber.chamber.

– Fuel injector nozzle isFuel injector nozzle is

also located in thealso located in the

combustion chamber.combustion chamber.

– Very common in dieselVery common in diesel

engines.engines.


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Throttle Body Fuel InjectionThrottle Body Fuel Injection

– Injectors are located in theInjectors are located in the

throttle body.throttle body.

– Throttle body is the intakeThrottle body is the intake

cavity or intake manifold.cavity or intake manifold.

– The Carburetor is removedThe Carburetor is removed

from the intake manifold andfrom the intake manifold and

simply replaced by a fuelsimply replaced by a fuel

injection system.injection system.

– Disadvantage: (1)Disadvantage: (1)


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Multi-Port (Point) Fuel InjectionMulti-Port (Point) Fuel Injection

– Uses one injector located:Uses one injector located:

• At the mouth of the intake

valve -or-

• At the mouth of an individualintake port that is connected to

only one intake valve.

– Much more efficientMuch more efficient

– Chrysler began this in theChrysler began this in thelate 70’s, Ford mid 80’s,late 70’s, Ford mid 80’s,

Chevy VortexChevy Vortex


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Methods of Fuel InjectionMethods of Fuel Injection

• Mechanical: (2)Mechanical: (2)

• Electronic Fuel Injection: (4)Electronic Fuel Injection: (4)

– Advantages: (9)Advantages: (9)


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Carb. Fuel Injection

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