SOLEX CARBURETTOR

Carburettory A carburettor is a device that blends Air and Fuel for

an internal combustion engine. y The process of formation of a combustible fuel air mixture by mixing the proper amount of fuel with air before admission to engine cylinder is called carburetion and the device which does this job is called a carburettor. y The goal of a carburetor is to mix just the right amount of gasoline with air so that the engine runs properly.

..y If there is not enough fuel mixed with the air, the

engine "runs lean" and either will not run or potentially damages the engine. y If there is too much fuel mixed with the air, the engine "runs rich" and either will not run (it floods), runs very smoky, runs poorly (bogs down, stalls easily), or at the very least wastes fuel. y The carb is in charge of getting the mixture just right.

The parts of a carb:y A carburetor is essentially a tube. y There is an adjustable plate across the tube called

the throttle plate that controls how much air can flow through the tube. You can see this circular brass plate in photo 1.

y At some point in the tube there is a narrowing, called

the venturi, and in this narrowing a vacuum is created. The venturi is visible in photo 2 y In this narrowing there is a hole, called a jet, that lets the vacuum draw in fuel. You can see the jet on the left side of the venturi in photo 2

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Different Modern carburetors1) Zenith Carburettor 2) Solex carburettor 3) Carter carburettor 4) S.U. carburettor

SOLEX CARBURETTORy It is most common type of carburetor which is used in

Fiat and standard cars. y It is famous for easy starting, good performance and reliability. y This is also provided with basic jets required for starting and normal running. y In addition to this, it is also provided with separate idling jet and accelerating

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PARTS LISTING FOR SOLEX CARBURETTOR

A* - Main Jet Cap b - Strangler Shutter Stop C - Throttle Spindle c1 - Strangler Shutter Spindle e - Body Assembling Screw Union F Float G* - Main Jet g* Auxiliary Jet H - Throttle Chamber Screw h - Carburettor Body j1 - Man Jet Carrier Washer J2 - Needle Valve/Filter Union Washers Seating J3 - Large Filter Union Washer

K* - Choke Tube L - Throttle Lever I - Strangler Lever O* - Float Chamber P - Swivelling Filter p - Float Needle Q - Filter Union Nut t* - Main Jet Carrier U - Choke Tube Fixing V - Butterfly v1 - Strangler Shutter X - Needle Valve

y It is a downdraught types of carburettor . y It have the provision for the supply of richer mixture

required for starting and y Weaker mixture for high speed running of the engine. y It consists of various fuel circuits such as starting , idling or low speed operation , normal running , acceleration etc.

1. Starting Circuit:y The throttle valve remains in closed position during starting .

The petrol is supplied to the starter petrol jet through first passage from the float chamber and the air through the starter air jet for starting operation. y Starting Valve which have different sizes hole,is made from flat disc. y The position of various holes can be adjusted in front of starter petrol jet by starter lever and then air is mixed coming from starter air jet.

y This air-fuel mixture, passes through another holes of

starter valve, in a passage of the carburettor, below the throttle valve. y The suction stroke of the engine sucks this mixture into the cylinder. y This mixture is rich enough to start the engine. y After the engine starts and speed increases, a weak mixture is required, therefore, a small hole of the starter valve is brought in front of the starter petrol jet by means of starter lever, there by reducing the quantity of petrol , which weaken the air-fuel mixture.

2. Idling And Slow Running Circuit:y During the idling operation, the throttle valve is kept

closed and the engine receives the mixture through a port opening below the throttle valve, whose area can be varied by an idle adjusting screw according to the need of the engine. y The petrol is supplied to a pilot petrol jet from the main jet fuel circuit through fourth passage and the air from a pilot air jet . y The petrol and air thus supplied mix up in the idle passage and go to a port situated below the throttle valve from where the mixture is sucked by engine.

3. Normal Running Circuit:y At normal running speed, starting circuit is closed and

throttle valve is opened. y The normal running circuit consist of main jet which receives the petrol through second passage, from the float chamber as the throttle valve is opened sufficiently, the air is drawn through the venturi where the petrol mixes up with it forming a suitable mixture for the normal running of the engine. In this case, only throttle valve, governed the air-fuel ratio.

4. Accelerating Circuit:y The engine requires an extra rich mixture during

acceleration period. y To obtained extra rich mixture, the fuel is pumped under pressure into the main air passage or in the venturi through an injector. y Diaphragm pump is used to create pressure, which is actuated by a lever connected to the accelerator. y The pump sucks the petrol from the float chamber through the pump valve and forces it through third passage into the main passage through an injector above the venturi of the carburettor.