Zenith Carburetor – Construction and Working

Zenith Carburetor is a British carburetor which is used by many popular companies. It is produced by Zenith Carburetor Company and was founde in 1910.
In this carburetor there is no starting problem and also this carburetor provides rich mixture during high speed.

Following are the list of components in a Zenith Carburetor :-
1) Float Chamber
2) Main Line
3) Main Jet
4) Compensating Jet or Auxiliary Jet
5) Starting Jet
6) Reservoir or Auxiliary Chamber
7) Choke
8) Throttle Valve

Construction :-

In this carburettor, Float Chamber is connected to the Venturi via a Main Line. Main function of fuel chamber is to take fuel from the fuel tank. This fuel chamber has two balls, two floats and a spindle. There is choke which when closed restricts the air flow to the carburetor. A throttle Valve is a valve between the carburetor and the engine which opens when fuel is needed by the engine . Fuel from main line enters to form air fuel mixture through Main Jet. Apart from main jet, there is a compensating jet also which compensate when more fuel is needed by engine at high speed.This compensating jet gets fuel from reservoir or auxiliary valve . Apart from compensating jet, it also has starting jet which aids engine at time of starting. It also gets fuel from reservoir or auxiliary valve.

Working :-

At first fuel from fuel tank enters into Float Chamber through a passage which is blocked by a spindle present in the float chamber when fuel is not needed. This spindle moves up and down to block and unblock the fuel supply to fuel chamber.
When the fuel supply to fuel chamber decreases the two floats come down and the two balls also come down with them. As the balls and the spindle are connected like a Seesaw, so when the balls come down the spindle comes up and fuel passage to fuel chamber is unblocked.
On other hand, when the fuel supply increases in the fuel chamber the two floats come up and the balls also come up. As the balls come up , the spindle comes down due to Seesaw connection between the balls and the spindle. When spindle comes down the passage is blocked and the fuel supply to fuel chamber stops.

Working at Low Speed:-
At low speed when choke is open, the air passes through the venturi where the velocity of air increases and pressure decreases. Since there is high pressure due to atmospheric pressure in fuel chamber and there is low pressure near venturi . So fuel flows from high pressure to low pressure i.e from fuel chamber through main line and comes out to mix with air from Main Jet. This fuel mixes with air coming from choke to form a mixture. This mixture has a ratio of 15:1 where air is 15 and fuel is 1. Then this mixture reaches the engine after passing through the throttle valve which is opened very little at low speed.

Working at high Speed :-
At high speed of vehicle the speed of engine increases, hence producing higher suction. Due to higher suction at venturi more fuel is supplied by main jet and fuel is also supplied by compensating jet or auxiliary jet. This auxiliary jet get fuel from auxiliary valve. But the compensating jet can supply fuel for only sometime because the fuel stored in auxiliary valve or reservoir is less and empty at high speed. This reservoir takes time to store the fuel because there is an orifice between the reservoir and fuel chamber. Very less fuel is allowed to pass from fuel chamber to reservoir due to orifice. So at high speed fuel is sprayed from main jet as well as compensating jet for sometime.

Working at time of starting :-
At time of starting, throttle valve is almost at closed position. There is very little gap for the fuel to pass in throttle valve at time of starting. For starting a rich mixture is needed by the engine.
The air from air filter passes through the gap in side of throttle valve and as the air passes through the gap, velocity of air increases and pressure of air decreases on the upper side of throttle valve and thereby producing suction effect at Starting jet which is placed at top of throttle valve. This starting jet also gets fuel from the same reservoir from where the compensating jet gets fuel. Then fuel is sprayed by starting jet and mixes with air present above throttle valve to form a rich mixture. The ratio of air to fuel in this rich micture is 11:1. This rich mixture reaches the engine and helps the engine to start.

These are the working of Zenith Carburetor in different situations.

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