How does a Solex Carburetor Work?

A Solex carburetor is a type of carburetor that is widely used in automobile vehicles. It was designed and manufactured by Solex, a French carburetor company. It was popular in European cars during the 1950s and 1960s and was also used in many other applications, including motorcycles, boats, and airplanes.

Solex carburetor

Solex carburetor
Solex carburetor.


The Solex carburetor is extensively used in most passenger cars and commercial vehicles like Hindustan, Ambassador, Premier Padmini, Standard, Herald, Jeep C.J. 3B, Jeep 150, 160, Standard 20, Bajaj biking, Dodge, Fargo 1.5 tonnes, and the Vanguard and in most foreign cars. The solex carburetor is a down draught type carburetor. It consists of devices for starting, idling, normal running, and acceleration.

The Solex carburetor works by mixing air and fuel correctly before delivering the mixture to the engine’s combustion chamber. It achieves this by using a series of jets, valves, and passages to control the flow of fuel and air into the engine. It is described in brief as follows: 

How does a Solex carburetor work?

How does a Solex carburetor work?
Solex carburetor diagram


Solex carburetor works by mixing air and fuel correctly before delivering the mixture to the engine’s combustion chamber. Here is a basic explanation of how it works:

The air enters the carburetor through an air intake and passes through a filter to remove impurities. The air then flows through a narrow passage called the Venturi, which creates a low-pressure area that draws fuel from the carburetor’s float bowl.

Fuel is delivered to the Venturi through a jet, which regulates the amount of fuel that is mixed with the incoming air. The air and fuel mixture then flows into the engine’s intake manifold and is distributed to each cylinder for combustion. The carburetor also has various other components, such as a throttle valve, which regulates the flow of air entering the engine, and an idle circuit, which provides the engine with fuel when it is idling.

The Solex carburetor design is relatively simple and consists of fewer moving parts than other carburetors, which makes it more reliable and easier to maintain. However, it does require periodic adjustments to ensure that the air-fuel mixture is correct for efficient engine performance.

Starting device for Solex carburetor- 

This figure shows the starting device for the Solex carburetor. It consists of a starter valve in the form of a flat disc having holes of different sizes. These holes connect the petrol jet and starter jet sides to the passage which opens into the air horn just below the throttle valve. 
Starting device for Solex carburetor.
Starter for solex carburetor.

How does a starting device for a solex carburetor work?

The starter lever is operated by the driver from the dashboard, which adjusts the position of the starter valve so that either bigger or smaller holes come opposite the passage. At the time of starting, a bigger hole connects the passage so that more fuel may go to the engine. The throttle valve is closed, and the whole of the engine suction is applied to the starting passage 1 so that the petrol from the float chamber passes through the starter petrol jet and rises into passage 2, some of it comes out and mixes with the air entering through the air jet. This air-fuel mixture is rich enough for starting the engine. 
After the engine has started, the starter lever is brought to the second position, so that smaller holes connect the passage reducing the amount of petrol. In this position, the throttle valve is also partly open, so the petrol comes from the main jet. The reduced mixture supply from the starter system in this situation is. However, sufficient to keep the engine running. When the engine reaches the normal running temperature, the starter is brought to the “off” position. 

Idling or low-speed operation for Solex carburetor- 

At idling or low speed, the throttle valve is almost closed. The engine suction is applied to the pilot petrol jet which supplies petrol. The jet itself draws petrol from the main jet circuit. The air is drawn from the pilot air jet. The air and petrol mix in the idle passage. The mixture comes out of the idle port which opens below the throttle valve. 
Idling or speed operation for Solex carburetor.
Idling or low-speed operation.
Slow speed openings are provided on the venturi side of the throttle valve, to ensure a smooth transfer from the idling circuit to the main jet circuit, without the occurrence of float speed. When the throttle valve is opened wide, the suction decreases at the idle port and is applied at low-speed openings. 

Normal running- 

During normal running, the throttle valve is partly opened and the engine suction is applied to the main jet, which supplies the fuel. The air enters directly through the venturi and mixes with the fuel. The air-fuel mixture is governed by the throttle valve. 


For acceleration, extra fuel is required by the engine, which is supplied by a membrane pump. The pump lever is connected to the accelerator. When the accelerator pedal is depressed, the pump lever presses the membrane forcing the fuel into the main jet. When the pedal is returned, the membrane moves back, sucking the fuel from the float chamber through the ball valve. 

Advantages of Solex carburetor- 

The Solex carburetors have several advantages over any other carburetors- 
  • Solex carburetors are simple in design. 
  • The Solex carburetor is designed to provide the correct air-fuel mixture to the engine, which helps to improve fuel efficiency.
  • Due to its simple design, the Solex carburetor is generally more reliable and less prone to malfunction than other carburetors. They are also very smooth in operation. 
  • The Solex carburetor is generally less expensive than other types of carburetors, which makes it a cost-effective option for small engines.

Disadvantages of Solex carburetor- 

There are several disadvantages of solex carburetors- 
  • Solex carburetors have improperly seated needle valves. 
  • Solex carburetors have cold starting issues. Starting operation is irregular because the starting jet is obstructed by the starting device control travel has shortened. 
  • Clogged jets or passages can harm the Solex carburetor to start even in warm conditions. 
  • Solex carburetors have initial pick-up problems because of obstructed main jet or emulsion orifices or insufficient acceleration pump. 


Solex C 32 PBIC carburetor is used in Fiat 1100 cars. It measures prompt starting from the cold regular running of the engine at low speeds when still cold. It must be left engaged until the rated operation temperature is reached. 
In this article, I discuss the Solex carburetor, its working principle, advantages, and disadvantages. I hope you like this article. 
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