Page 114 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Choke Circuit: When the engine is cold, the engine needs mixture. A disc called choke valve is fitted in the
front part of the carburetor from where the air enters. By closing it a little, less air from outside enters the engine
through the carburetor. When the engine is rotated to start, a lot of vacuum is created inside the carburetor, due
to which a lot of petrol comes out of the float bowl and goes into the inlet manifold and due to the rich mixture, it
starts quickly.
The driver can open or close this choke from his seat itself with the help of a flexible cable.

If this choke is accidentally left in the closed position, then combustion will not be complete due to the rich mixture
going inside the engine. Therefore, the choke valve should be opened after starting the engine.
Sometimes a small spring loaded valve is fitted in the choke disc, which opens when the vacuum in the carburetor
increases when the choke is closed. Through this some fresh air can enter the carburetor.
In another system there is a spring fitted on the choke shaft which keeps it closed in the full choke position, but
as the engine speed increases the pressure difference exerts so much pressure on the choke valve that it opens
the choke valve against the tension of the spring.

Petrol fuel system and its components such as fuel tank, mechanical fuel pump, electric pump, fuel filters

Petrol fuel supply system diagram

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CITS : Automotive - Mechanic Diesel - Lesson 29 & 30 CITS : Automotive - Mechanic Diesel - Lesson 29 & 30