A carburetor performs this function mechanically; relying on differences in air pressure inside the carburetor to regulate fuel flow.

1. BASIC AUTOMOBILE TECHNOLOGY
ENT2242
A SIMPLE OR ELEMENTARY CARBURETOR/EFI
SYSTEM
Group No: 09
MADANAYAKA N.M. ET/2016/068
MUNASINGHE P.T.G.R.H. ET/2016/009
SANDARUWAN S.A.D. ET/2016/083
SAJARUPAN T. ET/2016/023
GUNAWARDENA K.L.R.T. ET/2016/053
AHAMED A.J.S. ET/2016/037

2. Contents
1. Introduction .................................................................................................................................................. 3
1.1 History of the carburetor.................................................................................................................... 3
1.2 How does carburetor works............................................................................................................... 3
1.3 What is the basic requirements of the carburetor.............................................................................. 4
2. Types of carburetor....................................................................................................................................... 5
2.1 Natural draft carburetor..................................................................................................................... 5
2.2 Updraft carburetor.............................................................................................................................. 5
2.3 Downdraft carburetor: ....................................................................................................................... 5
2.4 Float type carburetor:......................................................................................................................... 5
3. Main parts of the carburetor........................................................................................................................ 6
3.1 Float chamber ..................................................................................................................................... 6
3.2 Fixed venture ...................................................................................................................................... 6
3.3 Variable venture ................................................................................................................................. 6
3.4 Trottle valve........................................................................................................................................ 6
3.5 Chalk valve .......................................................................................................................................... 7
4.1 How EFI Systems and Carburetors Work ................................................................................................... 7
4.2 Basic injection ..................................................................................................................................... 8
4................................................................................................................................................................. 9
4.4 Types of EFI System............................................................................................................................. 9
Engine management................................................................................................................................. 9
Benefits of EFI ......................................................................................................................................... 10
5. Carburetor vs Fuel injecting system....................................................................................................... 12
5.1 Advantages and Disadvantages of carburetor................................................................................. 12
5.2 Different between carburetor and fuel injection? .......................................................................... 12
6. Carburetor failure ....................................................................................................................................... 13
7. Carburetor rebuilding ................................................................................................................................. 13
Reference ........................................................................................................................................................ 14

3. 1. Introduction
A carburetor is a device that mixes fuel and air together and delivers the mixture to the
intake manifold of an internal combustion engine. Early carburetors achieved this by simply
allowing air to pass over the surface of the fuel (i.e. gasoline), but most later dispensed a
metered amount of fuel into the air stream.
Carburetion was the dominant method of mixing fuel and air for internal combustion
engines until the 1980s, when emissions regulations and concerns about fuel efficiency
resulted in fuel injection taking over. Although carbs were used in the United States,
Europe, and other developed nations through the middle of the 1990s, they made use of
increasingly complex control systems to meet emissions requirements
1.1 History of the carburetor
Different types of carburetors were developed by a number of automotive pioneers,
including German engineer Karl Benz, Austrian inventor Siegfried Marcus, English
polymath Frederick W. Lanchester, and others. Since so many different methods of mixing
air and fuel were used in the early days of the automobile, and earlier, stationary gasoline
engines also used carburetors, it’s somewhat difficult to pinpoint who “invented” the device.
These early carbs also differed in their basic method of operation from the “modern” carbs
that were dominant throughout much of the 20th century. This is due to the fact that historic
carb designs can be broken into two main types with an endless cavalcade of variations:
 surface carburetors
 spray carburators
1.2 How does carburetor works
Fuel enters the carburetor through a fuel inlet. The float
regulates how much fuel to let in. When the float bowl
has enough fuel the float moves up and shuts off the fuel
via the needle valve. As the fuel level drops, the float
drops down and allows the needle valve to open.
Fuel enters the carburetor throat through a main
discharge passage. Fuel is drawn by the vacuum created
in the carburetor bore. The fuel is then mixed with air
that is drawn in from the top of the carburetor bore, facilitated by the venturi. When the
engine is cold the choke valve is partially closed restricting the air flow. This richens up the
air/fuel mixture allowing the engine to start & idle cold.

4. The throttle valve is used to restrict the
air/fuel flow. It starts at a closed position
and as it is opened by the throttle linkage
the air/fuel mixture is allowed into the
intake manifold.
The idle circuit is built into carburetors so
that your engine can idle without dying.
When the throttle valve is closed when at a
stop there is little to no air going into the
intake manifold. If it wasn't for the idle
circuit, the engine would die.
As you can see in the illustration fuel is fed through the low speed jet and down to the idle
screw port using the strong vacuum being created below the throttle valve. Air is introduced
and mixed with the idle fuel using some sort of air bleed.
Note that once the throttle valve opens, the idle circuit is bypassed, so be sure you are doing
your idle mixture adjustment at idle speed.
When the throttle valve is opened a bit, but the RPM is
still low, most carburetors will allow a bit more fuel
into the intake via auxiliary holes.
1.3 What is the basic requirements of the carburetor
a) Reliable, durable and simple in maintenance and repair
b) Smooth operation at varying load
c) Good acceleration
d) Must be able to give full immediately after starting
e) Sufficient at high speeds
f) Good fuel economy
g) Even at low temperature, ease of starting
h) Steady operation at low idling speeds

5. 2. Types of carburetor
2.1 Natural draft carburetor
The natural draft carburetor is also known as side draft. If
there is less space on the top of the engine at that case this
type of carburetor is used. The air must enter horizontally
into the manifold.
2.2 Updraft carburetor
In this type of systems gravity fed fuel supply is used. The
carburetor is place above the fuel tank. By using the
gravity the tank receives the fuel. In the engine the air fuel
mixture must be forced upwards.
2.3 Downdraft carburetor:
The downdraft carburetors operate at the lower air velocities and
larger passage. In this the gravity assists the air fuel mixture flow to
the cylinder. This carburetor can deliver large measurements of fuel
when required for high power output and high speed.
2.4 Float type carburetor:
The float is a small closed vessel made up of a plastic or
brass. In this carburetor maintains a constant level of fuel in
the float bowl. The float works much like one in a watering
system, opening and closing a needle valve as the float
lowers or raises.

6. 3. Main parts of the carburetor
3.1 Float chamber
A float chamber is a device for automatically
regulating the supply of a liquid to a system. It is
most typically found in the carburettor of an internal
combustion engine, where it automatically meters
the fuel supply to the engine. However, this
arrangement is found in many automatic liquid systems, for example the
cistern of most toilets could be said to be a type of float chamber.
3.2 Fixed venture
Fixed venturi is used to varying the air velocity, as the venturi alters the fuel flow.
This construction is employed in most of the carburetors that was found on cars.
3.3 Variable venture
Variable venturi is used to inject the fuel jet
that primarily differs by the slide. In the
constant depression carburetors, the
process is done by a void operated piston.
The vacuum operate piston, is connected to
a pointed needle which slides in to the fuel
jet. A fundamental version exists that is
commonly found on dirt bikes and
motorcycles. The needle and the slide
must be directly controlled with the help of
the throttle position
3.4 Trottle valve
A throttle is the mechanism by which fluid flow is
managed by the constriction or obstruction.
An engine's power can be increased or decreased
by the restriction of inlet gases (by the use of a
throttle), but usually decreased. The term throttle
has come to refer, informally, to any mechanism
by which the power or speed of an engine is
regulated, such as a car's accelerator pedal. What is
often termed a throttle (in an aviation context) is
also called a thrust lever, particularly for jet engine powered aircraft. For a steam
engine, the steam valve that sets the engine speed/power is often known as a
regulator.

7. 3.5 Chalk valve
In an internal combustion engine, a choke valve modifies the air pressure in the
intake manifold, thereby altering the ratio of fuel and air quantity entering the engine.
Choke valves are generally used in naturally aspirated engines with carburetors to
supply a richer fuel mixture when starting the engine. Most choke valves in engines
are butterfly valves mounted in the manifold upstream from the carburetor jet to
produce a higher partial vacuum, which increases the fuel draw.
In heavy industrial or fluid engineering contexts, a choke valve is a particular design
of valve with a solid cylinder placed inside another slotted cylinder.
4.1 How EFI Systems and Carburetors Work
Carburetors provide
fuel control by purely
fluid dynamic means,
utilizing jets and
similar for the engine
to run smoothly and
efficiently it needs to
be provided with the
right quantity of
fuel/air mixture
according to its wide
range of demands.
For the engine to run
smoothly and
efficiently it needs to
be provided with the right quantity of fuel/air mixture according to its wide range of
demands.
Traditionally, the fuel/air mixture is controlled by the carburettor, an instrument that
is by no means perfect.
Its major disadvantage is that a single carburettor supplying a four-cylinder engine
cannot give each cylinder precisely the same fuel/air mixture because some of the
cylinders are further away from the carburettor than others.
One solution is to fit twin-carburettors, but these are difficult to tune correctly.
Instead, many cars are now being fitted with fuel-injected engines where the fuel is
delivered in precise bursts. Engines so equipped are usually more efficient and more
powerful than carburetted ones, and they can also be more economical, as well as
having less poisonous emissions.

8. 4.2 Basic injection
All modern petrol injection systems use indirect injection. A special pump sends the
fuel under pressure from the fuel tank to the engine bay where, still under pressure, it
is distributed individually to each cylinder.Depending on the particular system, the
fuel is fired into either the inlet manifold or the inlet port via an injector. This works
much like the spray nozzle of a hose, ensuring that the fuel comes out as a fine mist.
The fuel mixes with the air passing through the inlet manifold or port and the fuel/air
mixture enters the combustion chamber. Some cars have multi-point fuel injection
where each cylinder is fed by its own injector. This is complex and can be expensive.
It's more common to have single-point injection where a single injector feeds all the
cylinders, or to have one injector to every two cylinders.
The injectors through which the fuel is sprayed are screwed, nozzle-first, into either
the inlet manifold or the cylinder head and are angled so that the spray of fuel is fired
towards the inlet valve. The injectors are one of two types, depending on the
injection system. The first system uses continuous injection where the fuel is squirted
into the inlet port all the time the engine is running. The injector simply acts as a
spray nozzle to break up the fuel into a fine spray - it doesn't actually control the fuel
flow. The amount of fuel sprayed is increased or decreased by a mechanical or
electrical control unit - in other words, it is just like turning a tap on and off.
Electronic Fuel Injection system is controlled by a complex microprocessor control
unit (sometimes called an electronic control unit or ECU), which is basically a
miniature computer.This computer is fed with information from sensors mounted on
the engine. These measure factors such as the air pressure and temperature in the air
intake, the engine temperature, accelerator position and engine speed. All this
information allows an electronic system to meter the fuel far more accurately than the
simple mechanical system, which relies on sensing the airflow alone.
The computer compares the input signals from the sensors with information already
programmed into it at the factory, and works out exactly how much fuel should be
delivered to the engine. It then signals the on-off valve ig the injector to open and
squirt fuel into the inlet port. All this happens in a fraction of a second, the control
unit responding instantly to changes in accelerator position, temperature and air
pressure.
As well as improved control over fuel flow, the electronic system also operates at
lower pressure than a mechanical system - usually at around 25-30psi. This makes it
run more quietly than a mechanical system does.
A typical system is the Bosch LJetronic, which is fitted to a wide range of European
cars. In this system, fuel is drawn from the tank by an electric pump. It is then fed
straight up pipes to the injectors. The system pumps more fuel than is needed for
injection - a loop circuit returns the excess to the fuel tank via a pressure
regulator which keeps the pressure in the pipes constant.
The injector valves are held closed by springs, and opened
by solenoids(electromagnets) when signalled to do so by the control unit. The
amount of fuel injected depends on how long the solenoid holds the injector open.

9. 4.3 Typical sensors used in the electronic fuel injection (EFI) system
 Exhaust gas or oxygen sensor
 Engine temperature sensor.
 Air flow sensor
 Air inlet temperature sensor
 Throttle position sensor
 Manifold pressure sensor
 Camshaft position sensor
 Knock sensor
4.4 Types of EFI System
Merits of electronic fuel injection (EFI) system
 Improvement of volumetric efficiency of the engine
 Manifold wetting is eliminated due to direct fuel injection into the cylinder
 Atomization of fuel is independent of cranking speed, hence good atomization
even at low speed.
 Better atomization and vaporization results in less knocking.
 Formation of ice at throttle plate is eliminated.
 Distribution of fuel is independent of vaporization hence low volatile fuels can
also be used.
 Variation of air fuel ratio is almost negligible, which results in good engine
performance.
 Position of injection unit is not so critical, hereby height of engine can be less.
Demerits of electronic fuel injection (EFI) system
 High maintenance cost.
 Difficulty in servicing.
 Possibility of malfunction of some sensors.
Engine management
Some combined systems, known as engine management systems, can take into
account many more factors than an electronic fuel injection system. One type, the
Bosch Motronic, monitors the level of oxygen in the engine's exhaust gases. When
there is a deviation from normal, it can adjust both the ignition timing and the fuel
delivery to bring the engine back to tune. This ensures that pollution levels are cut to
a minimum as well as providing the best combination of performance and fuel
economy.

10. Benefits of EFI
1. Lower Fuel Consumption
EFI systems invariably produce lower fuel consumption than carbureted engines. This
follows from the sophistication of the electronic control system that constantly monitors
and adjusts the air/fuel ratio to maintain optimal combustion conditions. Small
carburetors tend to deliver a rich mixture (excessive fuel to air ratio) at both low power
output and at high power output. Carburetors are particularly inefficient when used in
varying power conditions, as it is difficult to optimize the air fuel ratio for all throttle
settings. Effective altitude compensation is difficult to achieve with carburetors, whereas
with EFI, altitude compensation is built into the system and works seamlessly. Whilst
the precise fuel consumption reduction will vary from engine to engine and duty cycle to
duty cycle, it is reasonable to expect a reduction in fuel consumption of 15% to 30%
following conversion of a carbureted engine to EFI. This applies to both two and four
stroke engines.
2. Works with Heavy Fuel
Currawong has a heavy fuel variant of its EFI system that capitalizes on the precision
fuel delivery performance of EFI. The heavy fuel system supports operation with Jet-A,
JP-5 and JP-8 fuels. It is extremely difficult to operate a small engine on heavy fuel
using carburetors, although attempts have been made by others to do this. EFI, in
conjunction with other proprietary advances, is the key to effective and efficient heavy
fuel operation.
3. More Power
EFI equipped engines generally provide higher power and torque than a carbureted version
of the same engine. It is difficult to optimize power and/or torque across a wide range of
engine speeds with carburetors, whereas EFI systems are capable of optimizing air/fuel
ratios and ignition timing over the whole range of operating speeds while at the same time
compensating for other factors in order to maintain optimum performance on a continuous
basis. Typically, EFI equipped engines produce around 5% to 10% more power than a
carbureted version of the same engine.
4. Enhanced Reliability
Engines equipped with EFI systems are inherently more reliable than carbureted engines.
This follows from the ability of the EFI control systems to maintain optimum air/fuel
ratios during all phases of flight. EFI systems are far less susceptible to icing, compared
to carburetors. Random engine stoppages, oiled spark plugs and other problems
associated with sub-optimal air fuel ratios are eliminated. Carburetors tend to go out of
tune. This necessitates constant adjustment and a significant risk of failure on long
missions due to drift in the settings. EFI engines on the other hand remain constantly in
the same state of tune. This not only improves reliability but also reduces the amount of
routine maintenance that is required.

11. 5. Excellent Starting
A major benefit of EFI systems is the greatly improved cold and hot starting
performance. This follows from the ability of the system to calculate the optimum
air/fuel mixture for starting as well as from the superior atomization that results from
injection of the fuel as compared to fuel delivery from a carburetor. Two stroke engines
are notoriously difficult to start in standard form, but with EFI they become as easy to
start as a four stroke. The ability of an engine to be started under a wide range of
operating conditions, from very hot to very cold ambient temperatures, from sea level to
high altitude and from engine temperatures that range from cold start to hot start is
vitally important in UAV operations. It is particularly critical to hybrid propulsion
systems where the engine may be stopped and re-started during flight.
6. Complete Altitude Compensation
Currawong EFI systems have been developed to have optimum altitude compensation.
Ambient air pressure is continually monitored and the ECU continuously calculates the
ideal air/fuel ratio for that altitude while also optimizing the air/fuel ratio for the other
variables (temperature, throttle position etc.). It is difficult to achieve altitude
compensation with carbureted engines, particularly where operation at varying altitude is
required. Invariably a compromise carburetor setting is required, meaning that at least
part of the time the air/fuel mixture is not optimal, resulting in excessive fuel
consumption when the mixture is over-rich in fuel and potential damage to the engine
when the mixture is over-lean.
7. Autopilot Integration
Because EFI systems are electronically managed, integration with on-board avionics
systems is not only possible, but is also widely applied. Flight controllers can digitally
control the throttle and ignition on/off. In addition, flight controllers receive real time
engine telemetry including RPM, temperatures, pressures, and fuel consumption. This
datas are enormously valuable for verifying the correct operation of the engine system
and maximizing the reliability of the whole aircraft. Off the shelf, our EFI systems are
integrated with the Cloud Cap Technology range of Piccolo Avionics. In addition,
through the open and fully documented API and the CANbus interface, the EFI system
can be readily integrated with other avionics.

12. 5. Carburetor vs Fuel injecting system
5.1 Advantages and Disadvantages of carburetor
Advantages
i. Carburetor parts are not expensive as that of fuel injectors, especially EFI,
which would give you large savings.
ii. With the use of carburetor you get more air and fuel mixture.
iii. In terms of road test, carburetors have more power and precision.
iv. Carburetors are not restricted by the amount of gas pumped from the fuel tank
which means that cylinders may pull more fuel through the carburetor that
would lead to denser mixture in the chamber and greater power as well.
Disadvantages
i. At a very low speed, the mixture supplied by a carburetor is so weak that it
will not ignite properly and for its enrichment, at such conditions some
arrangement in the carburetor is required.
ii. The working of carburetor is affected by changes of atmospheric pressure.
iii. It gives the proper mixture at only one engine speed and load, therefore,
suitable only for engines running at constant speed increase or decrease.
iv. More fuels are consumed since carburetors are heavier than fuel injectors.
v. More air emissions than fuel injectors.
vi. Maintenance costs of carburetor is higher than with fuel injection system.
5.2 Different between carburetor and fuel injection?
Carburetor
i. The air and fuel(petrol) enters the carburetor through separate ports assigned
for them.
ii. If undisturbed, they get mixed inside the carburetor at stoichiometric ratio can
get rich mixture by opening the choke valve.
iii. After mixing, the air-fuel mixture enters the cylinder through inlet valve
during suction stroke.
Fuel Injector
i. The fuel injection system consists of a fuel injector (nozzle) whose operation is
controlled by electric circuits through sensors. * The Electronic Control Unit
(ECU) is used for the control.
ii. The air from the air filter enters the cylinder through inlet valve during suction
stroke.
iii. The fuel injection begins at the end of compression stroke.
iv. The fuel is sprayed like moist.
v. Due to atomization, the air and fuel get mixed inside the cylinder.

13. 6. Carburetor failure
When a carburetor fails, the engine will run
poorly in certain conditions. Some carburetor
problems result in an engine that is unable to
run at idle without assistance, and others result
in various rough running conditions. The most
common issues are tied into cold engine
conditions, and a carburetor that works poorly
when an engine is cold may work just fine
when it is warm due to problems with the coke
or other components.
In some cases, carburetor problems can be
solved by manually adjusting the mixture or
idle speed. To that end, the mixture (which may
be either too lean or too rich) can typically be adjusted by turning one or more screws
that are attached to needle valves. These screws physically change the position of the
needle valves, which allows the amount of fuel to be reduced (resulting in a leaner
mixture) or increased (resulting in a richer mixture) depending on the situation.
7. Carburetor rebuilding
Many carburetor problems can be solved by making adjustments or performing other
fixes while the carb is still on the car, but other issues can only be dealt with by
removing the unit and rebuilding it. A carburetor rebuild operation typically involves
removing the unit, taking it apart, and cleaning it with a solvent that is designed
specifically for that purpose. A number of internal components, seals, and other parts
are then replaced before the unit is reassembled and installed.

14. Reference
http://www.crankshift.com/carburetor/#What_Does_Carburetor_Mean
https://www.carburetor-parts.com/How-a-Carburetor-Works_ep_1845.html
https://www.scribd.com/document/128400688/What-Are-the-Basic-Requirements-
of-a-Carburetor
https://www.mechgrid.com/carburetor-components-of-carburetor.html
https://www.quora.com/What-is-the-difference-between-a-carburetor-and-a-fuel-
injected-system
https://en.wikipedia.org
https://www.howacarworks.com/basics/how-a-fuel-injection-system-works