Solex Carburetor -Construction, Working and Advantages

Solex carburetor is a modification of simple carburetor. The simple carburetor works well in normal working conditions but it does not work well in conditions like winter and summer season, idle condition and high acceleration condition. In these conditions, Solex carburetor works well.
The main work of carburetor is to create air-fuel mixture in the right ratio.
Solex carburetor is known for its ease of starting the engine and the best performance of the engine.
Solex carburetor is a downdraught carburetor. In downdraught carburetor, the air enters from the top and leaves from the bottom.
The main drawback of simple carburetor is that it can not maintain different air-fuel mixture for different driving conditions but the Solex carburetor can provide different mixtures for different driving conditions.
This variation in air-fuel mixture for different conditions can be achieved by using Solex Carburetor. This Solex Carburetor can provide the rich mixture engine start and provide a lean mixture when traveling in economical speed with the vehicle. It can also provide different mixtures for different conditions like Engine Idling,Low-Speed operation, Acceleration etc.

Construction of Solex Carburetor:

In Solex Carburetor, the Fuel chamber is the part that collects fuel from the fuel tank and stores it to create air-fuel mixture in the carburetor. This fuel chamber has a float that is used to maintain the level of fuel in the fuel chamber.
There is a main line through which the fuel reaches the venturi throat tube. The fuel enters the venturi throat tube from the main jet which is located at the end of the main line. The fuel from the main jet gets air when the choke opens. Fuel from the main jet mixes with air which comes when the choke is opened to form air-fuel mixture and this air-fuel mixture reaches the engine cylinder when the throat valve opens.
Apart from the main jet, there are three more pipeline through which the engine cylinder gets fuel, they are pilot jet, pump jet, and starting passage.

Pump jet gets fuel from the acceleration pump and the pilot jet gets fuel from main jet. The pipeline of the pilot jet is separated from the main line.

The acceleration pump is operated using an acceleration pedal. This acceleration pump is used during acceleration.

A pilot jet is used during the idle or no-load condition. It has a pilot bleed orifice from which the pilot jet gets air to form an air-fuel mixture. Near the end of the idle condition pipeline, there is an Idling Screw which is used to control the amount of air-fuel mixture to be passed to the Engine Cylinder.

Starting passage gets its fuel from Starting Circuit or Bi-Starter. This starting circuit is used to supply the air-fuel mixture during the starting time. This starting circuit has a flat disc that has holes of different radius which is used to control the amount of fuel supply during starting. This starting circuit also has Air venturi which supply air in the starting circuit to create an air-fuel mixture. The air-fuel mixture from starting circuit is supplied to the engine cylinder through starting passage which is present below the throttle valve.


At first fuel from the fuel chamber enters fuel chamber through a passage that is blocked by a float when the required amount of fuel enters the fuel chamber.
The float which blocks the fuel tank and fuel chamber passage rises above as the level of fuel rises in the fuel chamber and it blocks the passage when fuel in the fuel chamber reaches its maximum level.

Working at the time of starting:-
At the time of starting, a rich mixture is needed by the engine. To provide a rich mixture at the time of starting Solex Carburetor has a starting circuit or Bi-Starter.
The main function of the Bi-Starter is to compensate for the problem that occurs while starting the engine, particularly in the winter season.
It provides a rich mixture to the engine at the time of starting. A rich mixture of air and fuel has a ratio of 11:1 where 11 part is air and 1 part is fuel. Normally air to fuel ratio required by the engine is 15:1 but at the time of starting it requires a ratio of 11:1 to start. This Bi-Starter has a flat disc and it has holes of different diameters.
The starter petrol jet and starter air jet are connected near the holes of the disc and the air-fuel mixture passes through the different holes of the starter disc to reach the engine in the suction stroke.
Through these holes the fuel and air pass from the Bi-Starter to the engine. This disc can be rotated manually using a starter lever so that it can be adjusted according to the fuel and air requirement. For example, a large hole of the disc will be used in the winter as more fuel will be required to start the engine in winter.

Working during Idling and Slow running of the engine:-
Idling is the condition when the vechile engine is running but the vechile is not in motion. This situation normally occurs when the vechile is stopped at red light and the engine is still on. At idle condition, there is no load on the engine but all the engine friction needs to be removed to keep the engine running.
During the idling condition or slow running condition, the throttle valve is completely closed. Since the throttle valve is closed, the suction created by the suction stroke is acted on a pilot jet directly.
Pilot jet is the jet that gets its fuel from the main line. The pilot jet pipe is connected to the main line and gets its fuel from it.
At the idling condition, the throttle valve is closed and proper pressure is not built to suck fuel from the main jet. So the suction stroke of engine directly sucks the air-fuel mixture from the pilot jet.
The fuel will be inducted from the pilot jet and it will be mixed with the air sucked from the pilot air-bleed orifice from the outside atmosphere.
The rich mixture from the pilot jet will be directly sent to the engine by a tube located just below the throttle valve.
There is an idling screw present near the opening of the pilot jet to control the speed of the engine by controlling the amount of air-fuel mixture to the engine.
A by-pass arrangement is also provided just above the throttle valve so that if the pressure is enough near the throttle valve to suck the air-fuel mixture from the by-pass arrangement. When this by-pass arrangement will be used the throttle valve will open a little bit. A less rich air-fuel mixture will be provided by by-pass arrangement so that the engine can run smoothly with the full movement of the air-fuel mixture.
The idle running condition works from 0 to 30 kmph speed and after that, it automatically stops.

Working during acceleration:
During the acceleration, there is load on the engine. Extra air-fuel mixture is required by the engine during the acceleration to give proper acceleration to the engine.
An additional acceleration pump injector is provided on the right side of the float chamber to provide the extra air-fuel mixture required during the acceleration.
An extra jet is provided on the top of the main jet to supply extra fuel supplied using the acceleration pump.
This acceleration pump is a diaphragm pump which is connected to a pedal. This acceleration pedal is also connected to the throttle valve through linkage.
When we will press the acceleration pedal, the acceleration pump will operate as well as the throttle valve will also open simultaneously.
As soon as the acceleration pedal is pressed, the acceleration pump will operate and will provide the extra fuel through the extra jet.
When the acceleration pedal is released the acceleration pump will suck fuel from the fuel chamber and store it to provide extra fuel for the next acceleration.

Advantages of Solex Carburetor:-

1) All circuits for different conditions works seprately.
2) It minimizes waste and reduce carbon formation.
3) Throttle response is high as compared to other carburetors.
4) It works perfectly under sudden heavy acceleration requirements.
5) It starts very easily.

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