Carter Carburetor: Construction, working and diagram

Diagram of carter carburator working
Diagram of Carter carburetor

Working of Carter carburetor, also its construction and working

Carter carburetor was invented by the founder of cast brass carburetor, William Carter. In the previous post, we have seen working of Solex carburetor, Carter carburetor is another type of modern carburetors.

Carter carburetor is a down-draught type carburetor. In Carter carburetor fuel or petrol enters into the chamber and air enters from the choke valve which is allocated at the top position. Choke valve keeps open during the normal running of the engine.

Visit: Solex Carburetor construction, working, and advantages

Working of Carter carburetor:

Unlike other carburetors, Carter carburetor has three venturies named as Primary, secondary and third main venturi. Primary venturi which is smallest among three venturies lies above the fuel level in the float chamber. Secondary and third main venturi lies below the fuel level in the float chamber as well as primary venturi. Suction presents at the primary venturi to draw petrol at low engine speed.

Fuel from the float chamber enters into the primary venturi using nozzle by making an angle in the upward direction as shown in the figure.

Now the mixture of air and fuel travels from primary venturi to the third main venturi through secondary venturi. From the main venturi, it finally travels to the engine cylinder for the combustion. Due to the use of multiple venturies, fuel reached the engine is in the atomized form which causes the smooth running of the engine apparently vehicle.

Fuel Circuit in Carter carburetor:

Fuel circuit in the Carter carburetor consists of the metering rod which is connected to the main throttle. Metering rod is used to control the amount of fuel drawn into the main engine.

Starting Circuit:

Starting circuit in the Carter carburetor consists of a butterfly valve which is also called a choke. When the choke is closed, the pressure at the nozzle is almost equal to the suction pressure. It creates a large pressure drop between the float chamber and the nozzle. Due to minimum air supply, the mass flow rate of the fuel increases rapidly. It results in the supply of rich mixture to the combustion chamber in the engine at the time of starting. In this way, Starting circuit works in the Carter carburetor.

Idling or No Load Running:

In idling condition, the engine requires a rich mixture for the combustion, also throttle valve remains closed in this condition. Throttle valve opens when speed increases slowly.


When we increase acceleration suddenly, we need required air-fuel mixture for the engine. For this required mixture, we use Acceleration pump circuit. When the engine is accelerated, plunger which connected to the inlet valve moves down and release the required extra into the choke tube through the jet.

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