Figure 1-26.—Venturi effect.Figure 1-27.—Throttle valve.of the throat is called the venturi (fig. 1-26). A tubecalled a discharge nozzle is positioned in the venturiand is connected to a reservoir of gasoline called thefloat bowl.The downward intake stroke of the piston creates apartial vacuum in the carburetor throat that allowslow-pressure air to rush by the fuel nozzle. This forcessmall drops of fuel to be mixed with the air. Then thefuel and air mixture must pass the throttle valve whichis controlled by the operator (fig. 1-27). The throttlevalve opens or closes to allow the correct volume of thefuel and air mixture into the engine. The choke valve(fig. 1-28) also controls the supply of fuel to the engine.When you start the engine in cold weather, the chokevalve can be partly closed, forming a restriction thatcauses more fuel and less air to be drawn into thecombustion chamber. This results in a richer air to fuelFigure 1-28.-Choke valve operation.1-20
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