assigmen dvi carburator

8/8/2019 assigmen dvi carburator

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How carburator works?

The carburetor works on Bernoulli's principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle linkage does not directly controlthe flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air

being pulled into the engine. The speed of this flow, and therefore its pressure, determines theamount of fuel drawn into the airstream.

Venturi Effect The carburetor, which is basically a large tube or Venturi . Vacuum created by the downward stroke of the pistoncauses the higher pressure in the floatchamber to force the fuel/air mixturethrough the fuel/air outlet passage (or

ports) in the carburetor venturi andvaporized, by the fast moving air stream. A needle sits in the hole toregulate the fuel flow. The throttlecable or engine vacuum operates theneedle up and down to regulate thefuel in the air stream.

Not all carburetors are as simple as theone above, some have more than one

hole fuel to be drawn from. Most all-modern carburetors have an idle speed adjustment screwit is actually a valve; the end of the adjustment screw is shaped like a needle and it regulates

fuel flow when the engine is running at low speed.

For higher speed operation a needle valve is attached to the slide, which is operated byvacuum or cable. In cases where the high-speed needle is attached to the slide, the slide israised and lowered by the throttle cable. When the throttle is open the needle is raised up outof the emulsion tube allowing more fuel to mix with in increased air allowed by the risingslide. As the throttle is closed the slide and needle come down reducing air and fuel.


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Most carburetors used on modernmotorcycles also have a movingflap in the venturi to regulate theairflow, a butterfly throttle valve(or throttle plate). On most

carburetors this is where thethrottle cable is connected. As thethrottle plate is opened it allowsmore air into the engine. Fuel isfed through a fixed orifice or jetcontrolling the amount of fuel inaddition to the idle port.

Some of the more expensive aftermarket carburetors and most of the newer orignal equipmentcarburetors have additional circuits or passageways and ports for fuel to enter the air stream.In addition to the idle circuit, a transfer, midrange or air circuits may be used to fine-tune thefuel mixture. Remember the idle port will provide fuel during the entire operation of thecarburetor. As the air speed increases the needle or main jet will add fuel in addition to theidle circuit.

The most modern carburetors are Vacuum controlled or CV (Constant Vacuum) type. Avacuum operated diaphragm controls the opening and closing of the slide (or piston). The CVCarburetor also has a butterfly throttle valve (or throttle plate).

At idle, with the throttle plate closed and the air streamcut off, idle speed is maintained by fuel metered throughthe slow jet. Air from the slow air jet mixes with the fueland is delivered to the idle port at the vacuum side of thethrottle plate. At low speed as the throttle plate iscracked open the transfer ports are exposed to thevacuum side of the throttle plate and additional fuel isdirected to the barrel of the carburetor. With throttle

plate cracked open a quantity of fuel also enters the air stream from the needle jet. The idle and transfer portssupply additional fuel to the carburetor barrel to assistduring the transition period from idle to mid range.

The venturi opening is reduced by the low position of the vacuum piston (Slide). This enablesinitial air stream velocities to be higher than normally attainable with fixed venturicarburetors. The higher air stream velocities provide greater quantities of fuel necessary for good acceleration.


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As the throttle plate is opened, airflow increases through the carburetor and the pressure dropin the venturi near the needle jet increases.

The low pressure in the venturi travels through the vacuum port in the vacuum piston to thechamber above the diaphragm. The chamber beneath the diaphragm is vented to atmospheric

pressure by a passage from the chamber to the carburetor inlet. The higher pressure at theunderside of the diaphragm overcomes spring pressure and moves the vacuum piston upwardin proportion to the pressure difference between chambers.

As the throttle plate is opened further, the pressure difference between the chambers aboveand below the diaphragm increases and the vacuum piston moves further upward. The venturiopening increases and the needle is lifted further out of the needle jet. The quantity of fuel andthe volume of air are simultaneously increased and metered to the proportions of enginedemand by the variable venturi and needle lift.

The accelerator pump is used to supply fuel during sudden or rapid throttle openings. Itquickly injects fuel into the venturi; the extra fuel provides for smooth acceleration andreducing throttle hesitation.

For cold starting carburetors are equipped with a choke or an enrichener circuit. The choke isa flap type valve similar to the butterfly or throttle plate. It is located on the inlet side of thecarburetor and reduces airflow making the fuel mixture richer. As the engine warms up thechoke is opened up and the carburetor returns to normal operation. An enrichener is a separatefuel circuit, manually controlled by a cable when it is engaged it provides additional fuelmaking the idle mixture richer.


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Carburator construction

y a base plate having a substantially planar surface including an opening adapted for connection to an air inlet passage of an internal combustion engine a throat member defining a fuel-air mixing passage mounted on said base plate having a mixture outlet

portion thereof in alignment with said opening in said base plate

y throat member having an air inlet portion spaced from said mixture outlet portion andincluding fuel aperture means extending through a wall portion thereof between saidair inlet portion and said mixture outlet portion and a fuel module mounted on said

base plate receiving said throat member including fuel channel means arranged anddisposed for communication with a source of fuel and with said aperture means in saidthroat member,

y fuel module including a metering pocket having an end surface having a meteringorifice defined therein forming a portion of said fuel channel means, fuel moduleincluding a rotatable adjusting plug received in said metering pocket having a spiralledge defining a metering surface lapping said metering orifice arranged for varyingthe flow area of said metering orifice in response to rotation of said plug

y said metering surface being biased into engagement with said end surface of metering pocket by means of a resiliently deformable ring engaging a shoulder formed on saidadjusting plug and a shoulder formed in said metering pocket.


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CARBURETOR .

A carburetor is basically a device for mixing air and fuel in the correct amounts for efficientcombustion. The carburetor bolts to the engine intake manifold. The air cleaner fits over the topof the carburetor to trap dust and dirt. The basic carburetor consists of the following parts:CARBURETOR BODY. The carburetor body is a cast metal housing for the carburetor components.

Usually the main body houses the fuel bowl, main jets, air bleeds, power valve, pump checks,diaphragm type accelerator pump, venturis, circuit passages, and float mechanism. The body isflanged on the bottom to allow the carburetor to be bolted to the intake manifold.

AIR HORN.

The air horn is also called the throat or barrel. It routes outside air into the engine intake manifold. Itcontains the throttle valve, the venturi, and the outlet end of the main discharge tube. The parts

which often fasten to the air horn body are as follows: the choke, the hot idle compensator, the fastidle linkage rod, the choke vacuum break, and sometimes the float and pump mechanisms.

THROTTLE VALVE .

This disc- shaped valve controls air flow through the air horn. When closed, it restricts the flow of airand fuel into the engine, and when opened, air flow, fuel flow, andengine power increase.

VENTURI.

The venturi produces sufficient suction to pull fuel out of the main discharge tube. A carburetorsystem or circuit is a network of passages and related parts that help control the air-fuel ratio underspecific engine-operating conditions.

The seven basic carburetor systems are the following:

1. FLOAT SYSTEM

2. IDLE SYSTEM

3. OFF IDLE SYSTEM

4. ACCELERATION SYSTEM

5. HIGH-SPEED SYSTEM

6. FULL-POWER SYSTEM

7. CHOKE SYSTEM


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Fl oat system

the float system maintains a steady working supply of gasoline at a constant level in the carburetor.This action is critical to the proper operation of the carburetor. Since the carburetor uses differences in

pressure to force fuel into the air horn, the fuel bowl must be kept at atmospheric pressure. The floatsystem keeps the fuel pump from forcing too much gasoline into the carburetor bowl. An excessivelyhigh float level will cause fuel to flow too freely from the discharge tube, causing an overlyrich mixture, whereas an excessively low float level will cause an overly lean mixture. The basic

parts of the float system are the fuel bowl, the float, the needle valve, the needle seat, the bowl vent,and the hinge assembly.

y The CARBURETOR FLOAT rides on top of the fuel in the fuel bowl to open and close theneedle valve. It is normally made of thin brass or plastic. One end of the float is hinged tothe side of the carburetor body and the other end is free to swing up and down

y The NEEDLE VALVE regulates the amount of fuel passing through the fuel inlet and theneedle seat. The needle valve is usually made of brass. Sometimes the end of the valve willhave a soft viton (synthetic rubber) tip. The soft tip seals better than a metal tip, especially if dirt gets caught in the needle seat

y The NEEDLE SEAT works with the needle valve to control fuel flow into the bowl. It is a brassfitting that threads into the carburetor body.

y The NEEDLE SEAT works with the needle valve to control fuel flow into the bowl. It is a brassfitting that threads into the carburetor body.

y he BOWL VENT prevents pressure or vacuum buildup in the carburetor fuel bowl. Withoutventing, pressure could form in the bowl, as the fuel pump fills the carburetor. This couldalso cause vacuum to form in the bowl, as fuel is drawn out of the carburetor and into theengine. On vehicles equipped with an evaporation control type emission system, the fuel


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bowl is vented into a hose going to a charcoal canister instead of the outside. The canisterstores toxic fuel vapors and prevents them from entering the atmosphere

Basic float system operation is as follows:

y When engine speed or load increases, fuel is rapidly pulled out of the fuel bowl and into the

venturi. This action causes the fuel to drop in the bowl. The needle valve also drops away fromits seat. The fuel pump can then force more fuel into the bowl.

y As the fuel level in the bowl rises, the float pushes the needle valve against its seat. When thefuel level is high enough, the float closes the opening between the needle valve and the seat bythe rising float, as the fuel reaches the desired level in the fuel bowl.

y With the engine running, the needle valve usually lets some fuel leak into the bowl. As a result,the float system maintains a stable quantity of fuel in the bowl. This is very important becausethe fuel level in the bowl can affect the air-fuel ratio


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Wh at is carburator

y Carburator is a device that blends air and fuel for an internalcombustion engine. It was invented by Karl Benz before 1885 and patented in

1886 in United Kingdom.y The word carburutor comes from the Frenchca meaning "carbide".Carburer

means to combine with carbon. In fuel chemistry, the term has the more specific

meaning of increasing the carbon (and therefore energy) content of a fuel by

mixing it with a volatile hydrocarbon.


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Idle Syst em

The carburetor idle system provides the air-fuel mixture at speeds below approximately 800 rpm or20 mph When the engine is idling, the throttle is almost closed Air flow through the air horn isrestricted to produce enough vacuum in the venturi. Since venturi vacuum is too low to pull fuel fromthe main discharge tube, the high intake manifold vacuum BELOW the throttle plate and the idle

circuit are used to feed fuel into the air horn.

The fundamental parts of the carburetor idle system include a section of the main discharge tube, alow- speed jet, an idle air bleed, a bypass, a idle passage, an economizer, an idle screw port, and anidle mixture screw.

y The LOW-SPEED JET is a restriction in the idle passage that limits maximum fuel flow in theidle system. It is placed in the fuel passage before the idle air bleed and economizer.

y

The IDLE AIR BLEED works with the economizer and bypass to add air bubbles in the fuelflowing to the idle port. The air bubbles help break up or atomize the fuel. This makes theair-fuel mixture burn more efficiently once it is in the engine.

y The IDLE PASSAGE carries the air-fuel slurry (mixture of liquid and air bubbles) to the idlescrew port.

y The IDLE SCREW PORT is an opening into the air horn below the throttle valve.

y The IDLE MIXTURE SCREW allows adjustment of the size of the opening in the idle screwport. Turning the screw IN reduces the size of the idle port and the amount of fuel enteringthe horn. Turning the screw OUT increases the size of the idle port and enriches the fuelmixture at idle.


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Most modern carburetors have sealed idle mixture screws that are NOT normally adjusted. Theseal prevents tampering with the factory settings of the idle mixture. Sometimes a plastic limiter capis pressed over the idle mixture screws. They restrict how far the screws can be adjusted toward therich or lean settings. Correcting idle screw adjustment on modern carburetors is critical toproper exhaust emission.

The basic operation of the idle system is as follows:

At idle, fuel flows out of the fuel bowl, through the main discharge tube, and into the low-speed jet. The low-speed jet restricts maximum fuel flow.

At the bypass, outside air is pulled into the idle system.

This partially atomizes the fuel into slurry.

As the air and fuel bubbles pass through the economizer, the air bubbles are reduced insize to further improve mixing.

The fuel and air slurry then enters the idle screw port. The setting of the idle screwcontrols how much fuel enters the air horn at idle.

With the throttle plate closed, high intake manifold pressure pulls fuel out of the idlesystem


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Off Idle Syst em .

The off idle, also known as the part throttle, feeds more fuel into the air horn when the throttle plateis partially open. It is an extension of the idle system. It functions above approximately 800 rpm or20 mph. Without the off idle system, the fuel mixture would become too lean slightly above idle.

The idle system alone is not capable of supplying enough fuel to the air stream passing through the

carburetor. The off idle system helps supply fuel during the change from idle to high speed

Basic off idle system operation is as follows:

The driver presses down on the accelerator and cracks open the throttle plate. As thethrottle plate swings open, the off idle ports are exposed to intake manifold vacuum.

Vacuum then begins to pull fuel out of the idle screw and the off idle port. This actionprovides enough extra fuel to mix with the additional air flowing around the throttle plate


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Accele ration Syst em

The carburetor acceleration system, like the off idle system, provides extra fuel when

changing from the idle system to the high-speed system. The acceleration system squirts a stream of

fuel into the air horn when the fuel pedal is pressed and the throttle plates swing open. Without theacceleration system, too much fuel would rush into the engine, as the throttle quickly opened. Themixture would become too lean for combustion and the engine would STALL or HESITATE. Theacceleration system prevents a lean air-fuel mixture from upsetting a smooth increase in enginespeed.

The basic parts of the acceleration system are the pump linkage, the accelerator pump, thepump check ball, the pump reservoir, the pump check weight, and the pump nozzle.

y The ACCELERATOR PUMP develops the pressure to force fuel out of the pump nozzle and

into the air horn. There are two types of accelerator pumps piston and diaphragmtype

y The PUMP CHECK BALL only allows fuel to flow into the pump reservoir. It stops fuel from

flowing back into the fuel bowl when the pump is actuated.

y The PUMP CHECK WEIGHT prevents fuel from being pulled into the air horn by venturivacuum. Its weight seals the passage to the pump nozzle and prevents fuel siphoning.

y The PUMP NOZZLE, also known as the pump jet, has a fixed opening that helps control fuelflow out of the pump. It also guides the fuel stream into the center of the air horn.


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The basic operation of the acceleration system is as follows:

The pump piston or diaphragm is pushed down in the pump chamber, as the throttle plate isopened, forcing fuel through the outlet passage.

At the same moment, the pump check ball will seat, keeping fuel from being pumped backinto the float bowl.

The pump check weight will be forced off its seat, allowing fuel to pass to the pumpdischarge nozzle, and then discharged into the carburetor.

The pump piston or diaphragm is raised in the pumping chamber when the throttle plateis closed, causing the pump check weight to seat blocking the outlet passageway.

At the same time, the pump check ball is pulled off its seat and fuel is pulled into the pumpchamber from the float bowl.

The pump chamber is filled with fuel and ready for discharge whenever the throttle plate isopened.

The linkage between the accelerator pump and thethrottle cannot be solid. If itwere, the pump would act as a damper, not allowing the throttle to be opened and closed

readily. The linkage activates the pump through a slotted shaft When the throttle is closed,

the pump is held by its linkage. When the throttle is open, the pump is activated by beingpushed down by a spring that is called a duration spring. The tension of the duration springcontrols the length of time that the stream of fuel lasts. The spring is calibrated to specificapplications. Too much spring pressure will cause fuel to be discharged too quickly, resultingin reduced fuel economy. Too little spring pressure will result in the fuel being dischargedtoo slowly, causing engine hesitation.


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High-Sp eed Syst em .

The high-speed system, also called the main metering system, supplies theengine air-fuel mixture at normal cruising speeds. This system begins to function when

the throttle plate is opened wide enough for the venturi action. Air flow through thecarburetor must be relatively high for venturi vacuum to draw fuel out of the maindischarge tube. The high-speed system provides the leanest, most fuel efficient air-

fuel ratio. It functions from about 20 to 55 mph or 2,000 to 3,000 rpm.

The high-speed system is the simplest system. It consists of the high-speed jet, the

main discharge passage, the emulsion tube, the air bleed, and the venturi.

y The HIGH-SPEED JET is a fitting with a precision hole drilled into the center. This fittingscrews into a threaded hole in the fuel bowl. One jet is used for each air horn. The hole sizedetermines how much fuel flows through the system. A number is stamped on the high-speed jet to denote the diameter of the hole. Since jet numbering systems vary, refer to

the manufacturer s manual for information on jet size.

y The EMULSION TUBE and AIR BLEED add air to the fuel flowing through the main dischargetube. The premixing of air with fuel helps the fuel atomize, as it is discharged into the airhorn.

y The VENTURI is the hourglass shape, formed in the side of the carburetor air horn. One ortwo booster venturis can be added inside the primary venturi to increase vacuum at lowerengine speeds


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The basic operation of the high-speed system is as follows:

When the engine speed is high enough, air flow through the carburetor forms a high vacuumin the venturi. The vacuum pulls fuel through the main metering system

Thrott le clos ed T h rott le open

The fuel flows through the main jet that meters the amount of fuel entering the system. Thefuel then flows into the main discharge tube and emulsion tube.

The emulsion tube causes air from the air bleed to mix with the fuel. The fuel, mixed with air,is finally pulled out the main nozzle and into the engine .


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F u ll-P ower System.

The full-power system provides a means of enriching the fuel mixture for high-speed, high-power conditions. This system operates, for example, when the driver pressesthe fuel pedal to pass another vehicle or to climb a steep hill. The full-power system is anaddition to the high-speed system. Either a metering rod or a power valve (jet) can be usedto provide variable, high-speed air-fuel ratio.

A metering rod is a stepped rod that moves in and out of the main jet to alter fuel flow.When the rod is down inside the jet, flow is restricted and a leaner fuel mixture results.When the rod is pulled out of the jet, flow is increased and a richer fuel mixture results for more power output. The metering rod is either mechanical-linkage or engine-vacuumoperated.

y The MECHANICAL LINKAGE metering rod is linked to the throttle lever.Whenever the throttle is opened wide, the linkage lifts the metering rod out of the

jet. When the throttle is closed, the linkage lowers the metering rod into the jet.

y The VACUUM OPERATED metering rod that is controlled by engine vacuum isconnected to a diaphragm. At steady speeds, power demands are low and enginevacuum is high, and the piston pushes the metering rod into the jet against spring

pressure, restricting the flow to the discharge tube. When the load increases,vacuum decreases, causing the piston spring to lift the metering rod out of the jet,

progressively increasing the flow of fuel to the discharge tube.

V acuu m O pe rat ed M e t e ring


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A vacuum power jet valve, also known as an economizer, performs the same function asa metering rod; it provides a variable high-speed fuel mixture. A power jet valve consists of a fuel

valve, a vacuum diaphragm, and a spring. The spring holds the power valve in the normally OPENposition. A vacuum passage runs to the power valve diaphragm. When the power valve is open, it

serves as an extra jet that feeds fuel into the high-speed system.

When the engine is cruising at normal highway speeds, engine intake manifold vacuum ishigh. This vacuum acts on the power valve diaphragm and pullsthe fuel valve closed. No additional

fuel is added to the metering system under normal conditions; however, when the throttle plate isswung open for passing or climbing a hill, engine vacuum drops. The spring in the power valve canpush the fuel valve open. Fuel flows through the power valve and into the main metering system,adding more fuel for more engine power


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Chok e Syst em

When the engine is cold, the fuel tends to condense into large drops in the manifold, rather thanvaporizing. By supplying a richer mixture (8:1 to 9:1), there will be enough vapor to assure completecombustion. The carburetor is fitted with a choke system to provide this richer mixture. The chokesystem provides a very rich mixture to start the engine and to make the mixture less rich gradually,

as the engine reaches operating temperature. The two types of choke systems are the manual andautomatic.

y The manual choke system was once the most popular way of controlling the choke plate;however, because of emissions regulations the possible danger when used withcatalytic converters and technological advances in automatic choke systems, manual

chokes are not often used today. In the manual choke system, the choke plate is operated by

a flexible cable that extends into the operator s compartment. As the control is pulled out,the choke plate will be closed, so the engine can be started. As the control is pushed back in,the position of the choke plate is adjusted to provide the proper mixture. The following aretwo features that are incorporated into the manual choke toreduce the possibility of theengine flooding by automatically admitting air into the engine.

Manua l Chok e Syst em


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y A spring-loaded poppet valve that is automatically pulled open by the force of the engineintake strokes.

Spring- loa ded popp e t va lve


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y An off-center choke valve that creates a pressure differential between the two sides of thechoke plate when it is subjected to engine intake, causing it to be pulled open against theforce of spring loaded linkage

V acuu m pow e r je t

y Automatic chokes have replaced the conventional manual choke. They control the air-fuel ratio for quick starting at low temperature and also provide for the proper amount of choking to enrich the air-fuel mixture for all conditions of engine operation during thewarm-up period. An automatic choke system has a choke plate (valve), a thermostatic

spring, and other parts depending upon choke design.

Auto m atic chok e


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The choke plate is a butterfly (disc) valve near the top of the carburetor air horn. When the chokeplate is closed, it blocks normal air flow through the carburetor.

The thermostatic spring is a bimetal spring (spring made of two dissimilar metals) which may be usedto open and close the choke. The two metals have a different rate of expansion that make the springcoil tighter when cold and uncoils when heated. This coiling-uncoiling action is used to operate

the choke.

The basic operation of the automatic choke system is as follows: With the engine cold, thethermostatic spring holds the choke closed.

When the engine is started, the closed choke causes high vacuum in the carburetor air horn. Thispulls a large amount of fuel out of the main discharge tube. As the engine and thermostatic springwarm, the spring uncoils and opens the choke plate. This action produces a leaner mixture. A warm

engine will not run properly if the choke were to remain closed


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Various methods are used to control the warming of the choke thermostatic spring. The fourmethods of providing controlled heat to the thermostatic spring are as follows: electricity, engine

coolant, well-type heated, and exhaust manifold.

y ELECTRICITY uses an electric coil to heat the thermostatic spring. The heating coil is switchedon with the ignition switch. Some systems use a control unit that prevents power fromreaching the electric coil until the engine compartment reaches a desired temperature.

Ele ctric Chok e

y The EXHAUST MANIFOLD (fig. 4-36) uses heat from the exhaust manifold to heat thethermostatic spring. The exhaust heat is brought to the choke through the means of a

heat tube. The heat tube passes through the exhaust manifold, so as it takes in fresh air viathe choke stove, it picks up heat from the exhaust without sending any actual exhaust fumesto the choke mechanism.

Ex haust- m ani f o ld he at-tub e chok e


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When the choke system is operating during warm- up, the engine must run at a faster idlespeed to improve drivability and prevent flooding. To accomplish this, fit the carburetor with afast idle cam that is operated by linkage from the choke.

When the choke closes, the fast idle cam swings around in front of the fast idle screw. As aresult, the fast idle cam and fast idle screw prevent the throttle plate from closing. Engine idle speed

is increased to smooth cold engine operation and prevents stalling. As soon as the engine warms, thechoke opens and the fast idle cam is deactivated. When the throttle is opened, the choke linkageswings away from the fast idle screw and the engine returns to curb idle (normal, hot idle speed).

If for some reason the engine should flood when it is cold, a device is needed to open thechoke, so air may be admitted to correct the condition. This is accomplished by the choke unloader.The choke unloader can be either mechanical- or vacuum-operated

Fast IDL E ca m op e ration

A mechanical choke unloader physically opens the choke plate any time the throttle swingsfully open. It uses a metal lug on the throttle lever. When the throttle lever moves to the fullyopened position, the lug pushes on the choke linkage (fast idle linkage). This provides the operator ameans of opening the choke. Air can then enter the air horn to help clear a flooded engine (enginewith too much liquid fuel in the cylinders and intake manifold).


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A vacuum choke unloader (fig. 4-39). also called a choke brake, uses engine vacuum tocrack open the choke plate as soon as the engine starts. It automatically prevents the engine from

flooding.

Chok e un loa de r

Before the engine starts, the choke spring holds the choke plate almost completely closed.This action primes the engine with enough fuel for starting. Then as the engine starts, the intakemanifold vacuum acts on the choke brake diaphragm. The diaphragm pulls thechoke linkage andlever to swing the choke plate open slightly. This action helps avoid an overly rich mixture andimproves cold engine drivability.


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CONCLUSION

The advantages for each type of system of carburetor:

Basic system Advantages

Float system To maintain a steady working supply of gasoline at a const antlevel in the carburetor.

Idle system Provide the air fuel mixture at speed below approximately800rpm or 20mph.

Off idle system Feeds more fuel into the air horn when the throttle plate ispartially open.

Acceleration system Providing additional fuel when the change from an idle to highspeed systems.

High speed system Supply of air-fuel mixture in the engine cruise speed of music.

Full power system Provide a means of enriching the fuel mixture for high speed,high power conditions.

Choke system By supplying a richer mixture when engine is cold.

The advantages and disadvantages compare to fuel injection system:

Advantages

Carburetor Fuel Injection

Low cost The fuel is injected directly into the cylinder at just the right time

Being improved over the years More efficient and complete burn

First fuel system designed A new technology

Disadvantages

Carburetor Fuel Injection

Lower efficient High cost

Not inject the fuel at the right time Use more power

use for old model Only use with a new car Not complete burn the mixture


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The carburetor does, however, come with a host of disadvantages. Firstly, with the way theworld is moving toward lower gas emissions, driving a car with a carburetor engine may getyou locked up in certain countries. Secondly, fuel economy is definitely not something thatyou can expect from your standard carburetor. You would have to almost indefinitely betuning your carburetor engine to offset changing weather and atmospheric conditions.Finally, with the current unpredictable fluctuations in gas prices worldwide, maintaining acarburetor engine would eventually only be an option for car enthusiasts who are notadversely affected by erratic world markets.

ConclusionIts clear that steps being made in the development of fuel injection systems are paving theway for enhanced performance, reduced fuel emissions, and enhanced engine reliability.However, for the diehard carburetor fanatic who cannot substitute for the power high and

maximum power output thrill that only a carburetor engine can offer, I fully empathize.

4.0 - REFERENCE

y www.wikipedia.com y http://www.brighthub.com/diy/automotive/articles/51709.aspx#ixzz14tmtRpuM


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INTERNATIONAL COLLEGE OF

AUTOMOTIVE MALAYSIA

Name : Mohd Hafiz Bin Mond Isa

Matrix Number : 921119-01-5143-04-01

Programmed : Diploma In Vehicles Inspection

DVI 1013 Introduction To Vehicle Components

Title : 7-Type Of Carburetor System

Lecture Name : Khairul Amilin Bin Ibrahim

Date Of Submission : 12 November 2010


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LEARNING OUTCOMES

After complete the project, student should be able to:

Explain briefly the function of the carburetor

List all 7 type of carburetor system

Introduction To Carburator

1.1 ConstructionCarburetors have been around almost as long as the car itself. Its functionality can beexplained as a device that delivers the correct amount of fuel to the engine according to theair that is forced through the engine by atmospher ic pressure. The initial cost of a carburetor engine is almost five times cheaper than an electronic fuel injected one, althoughmaintenance costs could perhaps set one back a bit. The clear advantage of a carburetor engine is that it is not restricted by how much gas is pumped from the fuel tank. This meansthat any modifications to the cam in an attempt to make the engine "breathe better" will allowthe cylinders to pull more fuel through the carburetor resulting in a more dense explosivemixture in the combustion chamber. The end result unrivaled power!

The carburetor works on Bernoulli's Principle: the fact that moving air has lower pressurethan still air, and that the faster the movement of the air, the lower the pressure. The throttledoes not control the flow of liquid fuel. Instead, it controls the amount of air that flows through

the carburetor. Faster flows of air and more air entering the carburetor draws more fuel intothe carburetor due to the partial vacuum that is created.

A carburetor basically consists of an open pipe, a "throat" or "barrel" through which the air passes into the inlet manifold of the engine. The pipe is in the form of a venturi it narrowsin section and then widens again, causing the airflow to increase in speed in the nar rowestpart. Inside the venturi is a throttle slide this valve controls the flow of air through thecarburetor throat, thereby regulating engine power and speed.

Carburetor Theory: The carburetor sucks fuel out of the bowl by the venturi effect thatBernoulli figured out. This means forcing air through a narrowed "throat" (the venturi or narrowed tube through the carb) makes the air speed up. Fast moving air is lower inpressure than the outside air pressure. Since we maintain the fuel bowl at outs ide airpressure by venting it on top, the fuel in the float bowl is under the higher "outside air"pressure than the low pressure air rushing through the carb throat. A pipe runs from thebottom of the bowl, through the main jet, to the area of the fast rushing air where thepressure is lower. The "outside air" pressure in the float bowl pushes the fuel to the lower pressure area. That's the middle of the throat of the carburetor. The fast moving air rips off tiny droplets of fuel from the pipe which mix with the air and flow to the engine to burn.

assigmen dvi carburator

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