Table of Contents
What is Carter Carburetor | Diagram , Working
Carter carburetor is a downdraft carburetor. It is an American make carburetor and used in Jeep. Figure 2.24 shows a diagrammatic view of this carburetor. It consists of the following circuits.
(i) Float circuit
(ii) Starting circuit
(iii) Idle and low speed circuit
(iv) Part throttle circuit
(v) Full throttle circuit
(vi) Acceleration pump circuit.
The petrol enters the float chamber. The air enters the carb..sretor from the top and the choke valve in the passage remains open during normal running. This carburetor consists of three venturies. The smallest venturi i.e. primary venturi lies above the fuel leve’ in the float chamber. Other, two venturi’s are below the fuel level and one is below other. At very low speeds, suction in the primary venturi is adequate to draw petrol. The nozzle enters the primary venturi at an angle delivering the fuel upward against the air stream in an atomized form. The mixture from the primary venturi enters through the secondary venturi where it is surrounded by a blanket of air stream and it finally leads to mam venturi. In main venturi, again the fresh air supply insulates the stream from the second venturi. The mixture reaches
the engine iIllatomized form. Multiple venturies result the better formation of the mixture at very low speed causing steady and smooth operation at very low and also at very high speeds.
(i) Float circuit:
The float chamber contains float. The inlet needle valve operated by a float controls the supply of fuel from the fuel filter into float chamber.
(ii) Starting circuit:
The choke valve of usual type is used for starting purposes. During starting, the choke valve is in closed position; the whole of the engine suction is applied to the main nozzle which delivers the fuel. As the air flow is quite small, the mixture supplied is very rich.
(iii) Idle and low speed running:
For idling, a rich mixture of small quantity is required. During idling, a throttle valve is almost closed. The whole of the engine suction is applied to the idle port. Consequently, the petrol is drawn through the idle feed jet and air through first bypass and a rich mixture is supplied. In low speed operations, the throttle valve is opened. The main nozzle also starts supplying the fuel at this speed port through idle passage.
(iv) Part throttle circuit:
The throttle valve is opened further for increasing the speed. The fuel is delivered by the main nozzle only.
(v) Full throttle circuit:
Now, the throttle valve is fully opened. Maximum amount of air is passed through the venturi. The higher rate of fuel flow is required. It is achieved by means of the metering rod. Metering rod has two or more steps of diameter. The area of opening between metering rod jet and metering rod governs the amount of petrol drawn into the engine. The metering rod is connected to the accelerator pedal through linkage. When the accelerator pedal is pressed, the throttle is held wide open and simultaneously, the metering rod is lifted up. Hence, the smallest section of the rod is in jet and the maximum quantity of petrol flows out
(vi) Accelerating pump circuit:
The accelerating pump is used to overcome flat spot during acceleration. The construction of pump is similar to Figure 2.21 of “acceleration difficulty” in a previous topic. When the throttle is suddenly opened by pressing accelerator pedal, a pump will be actuated and a small quantity of petrol is spurted into the choke by an acceleration jet. Leaving the accelerator pedal causes the pump piston to move up thereby sucking of fuel from the float chamber for the next operation.
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