Induction System – carburetor Introduction A device used to mix or meter the fuel with air in proportion that satisfies the energy demands of the engine in all phases of operation Venturi vacuum is used to draw in the correct amount of fuel through a discharge tube. More fuel is drawn in as venturi vacuum increases, and less as the vacuum decreases Venturi Venturi is a streamlined restriction that partly closes the carburetor bore. Air is forced to speed up as it enters the venturi to pass through the restriction. Restriction causes the formation of a vacuum below the venturi. As engine speed increases during acceleration, more air is drawn into the carburetor

Induction System – carburetor Venturi

Induction System – carburetor Venturi

Induction System – carburetor Carburetion The three general stages involved in carburetion: 1. metering 2. atomization 3. vaporization Metering In process of carburetion, fuel is metered into the air passing through the barrel of the carburetor. Ideal air/fuel ratio is called the stoichiometric ratio (14.7 : 1) 1. If there is more fuel in the mixture, it is called a rich mixture. 2. If there is less fuel, it is called a lean mixture. The amount of fuel metered into the air is depend on: 1. amount of air passing through the carburetor 2. engine temperature 3. load and speed requirements 4. amount of oxygen in the exhaust stream.

Induction System – carburetor Carburetion Atomization - Stage where the metered fuel is drawn into the air stream in the form of tiny droplets through the discharge ports. Vaporization - Surface area, amount of surrounding air and venturi effect help to create a fine mist of fuel below the venturi in the bore - Swirl, turbulence, and heat within the intake manifold and cylinder also enhance vaporization.

Induction System – carburetor Purpose of Carburetor Supply a combustible mixtures for a spark ignition engine by atomize and vaporize the liquid petrol mixing it with the air in correct proportions to meet the engine requirement Allows the driver to control amount of air fuel mixture that enter the cylinder by the controlling the throttle plate Carburetor Classification There are several ways how the carburetors are classified Carburetor Draft – defined as the act of pulling or drawing air. There are three type of carburetor draft system: i. Down draft – air flowing vertically down into the engine ii. Side draft – air flows through the carburetor in a horizontal direction iii. Up draft – brings the air and fuel into the engine in an upward direction

Induction System – carburetor Carburetor Classification Carburetor Barrel – a passageway or bore used to mix the air and fuel. It consists of the throttle plate, venturi, and air horn. There are three type of carburetor barrels that use in automotive engine: i. single barrel – used on small engines that do not require large quantities of air and fuel ii. double barrels – two throttle plates and two venturis, both barrels and the size of barrel are different. iii. Four barrels – engine operates on two barrels during most driving conditions. When more power is needed, the other two barrels add fuel to increase the amount of horsepower and torque produced by the engine.

Induction System – carburetor Carburetor Classification Carburetor Venturi - streamlined restriction that partly closes carburetor bore Single venturi – simple carburetor Double (duo) venturi – has an additional secondary venturi located at the greatest restriction area of the next larger venturi (better vaporization and atomization – increase efficiency of the carburetor) Triple venturi – more control and atomization process (discharge tube feeds fuel into the smallest venturi for maximum control and atomization) Variable venturi – size of venturi depends on the throttle pedal movement

Induction System – carburetor Carburetor Classification Feedback or non feedback Feedback carburetor is electronically controlled. In many ways, the system is similar to electronic fuel injection. However, the electronic control module (ECM) sends pulses to a solenoid in the carburetor or a vacuum-controlled metering valve instead of to a fuel injector