Send current to the different spark plugs for a four

send current to the different spark plugs.
For a four cylinder engine the cam of the contact breaker has four lobes. Therefore, it makes and
breaks the contact of the primary circuit four times in every revolution of cam. Because of which
current is distributed to all the spark plugs in some definite sequence.
The primary winding of ignition coil has less number of turns (e.g. 200 turns) of thick wire. The
secondary winding has relatively large number of turns (e.g. 20,000 turns) of thin wire. When the
magnet rotates current is induced in the primary circuit. When the contact point is open, the
magnetic field collapses and the movement of the magnetic field induces current in the secondary
winding of ignition coil. As the number of turns in secondary winding are more, a very high voltage is
produced across the terminals of secondary.
Advantages
 Better reliability due to absence of battery and low maintenance.
 Better suited for medium and high speed engines.
 Modern magneto systems are more compact, therefore require less space.


Disadvantages
 Adjustment of spark timings adversely affects the voltage.
 Burning of electrodes is possible at high engine speeds due to high voltage.
 Cost is more than that of battery ignition systems.
FUEL SYSTEM
The fuel supply system of spark ignition engine consists of:
o Fuel tank
o Fuel filter
o Sediment bowl
o Fuel lift pump
o Carburettor
o Fuel pipes
o Inlet manifold
Fuel system for spark ignition engines
The fuel comes from the fuel tank to the fuel filter and then to the lift pump. From there the fuel goes to
the carburettor through suitable pipe. From the carburettor, the fuel goes to the engine cylinder, through
the inlet manifold of the engine.
In some system fuel flows from the fuel tank to the carburettor under the action of gravity A
transparent fuel filter is also provided to hold the dust and dirt of the fuel
Carburettor
The process of preparing an air-fuel mixture away from the cylinders of an engine is called carburetion
and the device in which this process take place is called carburettor.
Principle of carburettor:
The basic principle of all carburettor design that when air flows over the end of a narrow tube or jet
containing liquid, some liquid is drawn into the air stream. The quantity of liquid drawn into the air
stream increases as the speed of air flow over the jet increases and also the quantity is greater if the

tube is made larger.
Carburetor with pump feed to fuel reservoir
In practice, the fuel level in the jet is maintained by a float chamber. The fuel levels in the jet and in
the float chamber are always the same. As the fuel is consumed, the level in the float chamber goes
down. The float in the float chamber also goes down and the needle valve comes off its seat allowing
more fuel into the chamber from the fuel tank. When the fuel level rises to its correct level, the float
presses the needle valve back to its seat and cuts off the fuel flow. The velocity of the air flowing over