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greater than that prevailirg at low speed. The auxiliary air passages are sometimes controlled by means of reeds which open progress ively as more auxiliary air is needed or by a series of balls which close the auxiliary air ports. The strength of the reeds or the weight of the balls may be varied so the air passages will open progressively and admit more air as the demands increase.
Fig. 69.-Latest Holley Carburetor Has Fixed Air Intake and No
Auxiliary Air Valve.
Q. What is a multiple jet carburetor?
A. A simple form of multiple jet carburetor is shown at Fig. 68. In a device of this character, two or more spray nozzles are used instead of a single jet. The arrangement is usually such that the primary nozzle is used at low speed while the secondary nozzle is brought in action at higher speed when more fuel is needed. In some types the arrangement is such that the primary nozzle acts only at low speed while the secondary nozzle supplies gasoline only at high speed. In other multiple jet carburetors, the nozzles are brought into action progressively when the throttle is opened to
such a point that the primary nozzle, which has a small spraying orifice, cannot supply fuel enough; then the secondary nozzle is brought into action and contributes its quota of liquid to compensate for the augmenting demand of the engine.
Q. How is the simple type of carburetor adjusted?
A. In the simplest forms of carburetors, the amount of gasoline or other fuel supplied the mixture can be altered only by changing spray nozzles until one having the proper size hole to suit the conditions then prevailing is found. On some types, a slight degree of adjustment is provided by altering the float level, while in others the main or auxiliary air supply is varied.
Q. How are gasoline proportions usually regulated?
A. In most of the carburetors that have received general application, such as the types outlined at Figs. 69 and 70, the spray nozzle orifice is controlled by a needle valve which may be used to regulate the amount of gasoline entering the air stream.
Q. How is the amount of air varied?
A. In some forms of carburetors no provision is made for altering the amount of air supplied the mixture. This is usually the case in those forms where the auxiliary air supply ports are controlled by a series of reeds or balls. In the types where one valve regulates the aux liary air supply, the amount of air may be varied by increasing or decreasing the spring tension or by regulating the lift of the valve.
Q. How can one tell when the mixture is not correct? · A. There are two methods of determining poor mixture. If the engine action is irregular and the trouble is not due to ignition, or to defective motor parts, it can be ascribed to faulty carburetion. The exhaust gas also indicates if the mixture is too rich.
Q. How can one tell when there is too much gasoline in mixture by motor action?
A. An excess of fuel in the mixture will tend to make the motor overheat and be sluggish in action.
Q. What indicates an excess of gasoline in the mixture at the exhaust?
A. Clouds of black smoke issuing from the muffler or a foul smelling exhaust indicates that too much gasoline is present in the mixture. When there is an excess of liquid fuel and combustion is poor, the exhaust gases in addition to smelling very strong, will
have a tendency to affect the eyes of a person standing in the path of the discharging gas.
Q. What do clouds of white or gray smoke at the muffler indicate?
A. White or bluish white smoke means that too much lubricating oil is being used, while gray smoke indicates that in addition to a surplus of lubricating oil, there is too much gasoline in the mixture.
Fig. 71.-Sectional View of Schebler Model E Carburetor Showing
Auxiliary Air and Spray Nozzle Regulation.
Q. What shows an excess of air in the mixture?
ping back in the carburetor, and loss of engine power even if tbere are no popping sounds.
Q. When are the exhaust gases visible?
A. The exhaust gas as it issues from the end of the manifold or through the muffler cut-out fitting is clearly visible after dark.
Q. What color is the exhaust gas when mixture is correct?
A. If combustion is good the exhaust gas will be almost colorless and have the bluish tinge that is present in the flame of a ga burner of the Bunsen type or blue flame oil burner.