A carburettor is a device used in petrol or similar liquid fuel engines by means of which the fuel mixed with air,is supplied into the induction manifold of the engine.The main object of the carburettor is to supply the required quantity of fuel and Air mixture of the correct strength as dedicated by the load condition of the engine.
There are three important types of carburettor available in market,
The details about Zenith and Solex Carburettor was covered in earlier posts.In this post,you will find details about Amal Carburettor.
An Amal carburettor is used in small petrol engines which drives motor cycles and scooters.This carburettor is capable of maintaining a uniform mixture strength throughout the throttle opening range.This is done by means of a tapered needle,adjustably attached to the throttle valve.
Construction Of Amal Carburettor:-
This carburettor has following main parts,
01) Carburettor Body
02) Throttle Valve
03) tapered Needle
04) Throttle Valve Operating Cable
05) Main Jet
06) Pilot Jet
07) Chamber For Pilot Outlet And By-pass
08) Auxiliary Air Intake
09) Pilot Outlet
10) By-pass Outlet
11) Float Chamber
12) Jet Block
14) Needle Valve
15) Air Valve
16) Air Valve Operating Cable
A throttle valve is fitted in carburettor body,to which a tapered needle is attached.The combination of throttle valve and tapered needle is operated by means of operating cable.To set the air-fuel ratio,the position of this tapered needle can be adjusted with respect to the throttle valve.The tapered end of the needle,regulates the area of passage in the main jet,supplies fuel to a chamber who has pilot outlet and by-pass outlet.An adjustable auxiliary air intake is also supply air to this chamber.The pilot outlet and by-pass are situated in front and back side of the throttle valve respectively.
The float chamber is connected with jet block,which contains,main and pilot jet.The float governs the level of fuel in float chamber.The float chamber receives petrol from the oil tank through needle valve,attached to the float with the help of clip.The air valve,which can be operated independently by an operating cable,to obstruct the main air passage.An adjusting screw is provided on the wall of carburettor body,by which the position of the throttle valve can be preset independent of operating cable adjustment for idling purpose.
Working Of Amal Carburettor:-
The throttle valve remain closed at starting of engine.The engine draws the mixture of air-fuel through pilot outlet.This mixture carries excess fuel,such mixture is not desirable for normal running of the engine ,therefore,the throttle valve is to be slightly raised for admitting supply of air from the main air passage.
The more the throttle valve opened,the less will be the depression on the pilot outlet,but a higher depression will be created on the by-pass and now the mixture flows from this by-pass as well as pilot outlet to compensate for accelerating period.
The function of air valve to obstruct the main air passage at the time of the start which results in enriching the mixture by increasing depression of the main jet.
The mixture provided by the pilot outlet and by-pass system,is supplemented by the fuel from the main jet approximately at 13% of the throttle valve opening.After the 75% of the opening of the throttle,the main jet only provides the fuel regulation.
At the time of idling,the throttle stop screw provides a definite throttle opening for idling purpose.
By this way,air-fuel mixture is supplied to the engine cylinder of motor cycle at various operating conditions.
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Various Circuits In Solex Carburettor.
Construction And Working Of Zenith Carburettor.
Working Principle Of Simple Carburettor Used In Petrol Engine.