Solex Carburetor Working, Advantages Of Solex Carburetor

solex carburetor

🔗Design and working of simple carburetor
🔗Essential parts of modern carburetor and their functions

Solex carburetor construction and working

Solex carburetor is famous for its performance, reliability, and ease of starting. The figure shows a diagram of a downdraught solex carburetor. This type of carburetor has distinct fuel circuit for starting, idling, acceleration, low speed operations, etc. Provisions on solex carburetor ensure the supply of richer mixture at starting, and weaker mixture during cruising of the engine.

Figure shows different component of the solex carburetor. The bi-starter is helpful in cold starting of the engine and it is a unique device for solex carburetor.

The various component of solex carburetor and fuel and air circuits for various operations are described below

Cold starting and warming circuit

Bi-starter is the unique device incorporate with the solex carburetor for the easy cold starting. Bistarter valve, in the form of flat disc with holes (of different sizes) is connected to starter gasoline jet (4) and starter air jet (passage which opens just below the throttle valve at (5). The starter lever is used to positioning or shift the size of hole come opposite to the passage. Starter lever is operated by using the flexible cable from the dashboard controls.

Richer air-fuel mixture is required during starting, after starting the mixture is progressively leaned. While starting, throttle valve remains in closed position and bigger holes are positioned in bistarter. Then the whole engine suction is forced to starting passage. While suction passes through the starting passage, it carries air from air jet (5) and fuel from jet (4). The final output of starting passage is rich enough for starting.

After engine reaches some speed, the smaller holes brought in front of gasoline jet by using the lever. Thereby reduce gasoline amount and weaken the air-fuel mixture. Similarly, when engine reaches normal speed, the next small hole is brought in front of gasoline jet. Finally, the starter valve is completely closed by the starter lever.

Normal running circuit

In normal running speed, the bistarter circuit is closed and the throttle valve is opened. In normal running circuit, the fuel is supplied through the main metering jet from the float chamber. The fuel enters to the well of air-bleed emulsion system (1), then fuel sprays into the suction air in the venturi through the horizontal spraying nozzles (3) on the air-bleed emulsion system. The air correction jet (2) on the air-bleed emulsion system calibrate the incoming air and ensure the correct air-fuel ratio.

Idling and slow running circuit

In idling operation of the engine, the throttle valve is kept closed. The fuel flows from the well of emulsion system to the piolet jet. Fuel is then get mixed with little air through the piolet air-bleed orifice. This air-fuel mixture is then sent down below the throttle. Idling adjustment screw in this passage help to vary and set desired idling speed.

In order to a smoother transition from idle/low-speed operation to the main operation, a bypass orifice (6) is provided at the venturi side of the throttle. When the throttle opens gradually, the suction at idle port is reduced, but suction pressure is exerted at bypass orifice (6). This arrangement offset the reduction of suction at idle port.

Acceleration circuit

During acceleration of engine more fuel is required; diaphragm type pump is used to supply this extra fuel. When acceleration pedal is pressed, the pump connects to the pedal press pump diaphragm towards left. The diaphragm movement forces the fuel to pump injector (7) through the pump jet. When the accelerator is released, the pump lever pulls the diaphragm. The movement of diaphragm create a vacuum in diaphragm pump, and gasoline from float chamber is then sucked in to pump through the inlet valve.

Advantages of Solex carburetor


  • Separate circuit for different scenario. (Starting circuit, idling circuit, accelerating circuit, etc.)
  • Solex carburetor is tuned to change flow as per real requirement. This will reduce fuel wastage and reduce emission.
  • Ease of starting. The Bi-starter helps to cold starting of the vehicle.
  • Throttle response increase.
  • Solex carburetor has an additional pump circuit for sudden acceleration requirement.


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