Figure 1-26.—Venturi effect.

Figure 1-26.—Venturi effect. Figure 1-27.—Throttle valve. of the throat is called the venturi (fig. 1-26). A tube called a discharge nozzle is positioned in the venturi and is connected to a reservoir of gasoline called the float bowl. The downward intake stroke of the piston creates a partial vacuum in the carburetor throat that allows low-pressure air to rush by the fuel nozzle. This forces small drops of fuel to be mixed with the air. Then the fuel and air mixture must pass the throttle valve which is controlled by the operator (fig. 1-27). The throttle valve opens or closes to allow the correct volume of the fuel 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 choke valve can be partly closed, forming a restriction that causes more fuel and less air to be drawn into the combustion chamber. This results in a richer air to fuel Figure 1-28.-Choke valve operation. 1-20