Зображення сторінки
PDF
ePub

thinner mixture or one containing a larger proportion of air can be used to advantage at high engine speed. The automatic form of carburetor, which is the type generally used to-day, provides for the introduction of an auxiliary supply of air through a separate opening that will dilute the excessively rich mixture obtained at higher speed and make it more suitable as a combustible gas.

[merged small][graphic][subsumed][merged small][subsumed][merged small][subsumed][subsumed][subsumed][ocr errors]

Fig. 68.—Two Jet Carburetor of Simple Design.

Q. How may auxiliary air be admitted to the carburetor?

A. The auxiliary air passage may be controlled by any form of automatic valve. In the design shown in Fig. 67, the air is admitted by means of an ordinary spring seated mushroom or poppet valve. The spring tension is so proportioned that the valve will open only on medium and high engine speeds, at which times the suction is

greater than that prevailing 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.

[graphic][merged small][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

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

[graphic][merged small][subsumed][subsumed][subsumed][merged small][subsumed][subsumed]

Fig. 70.-Sectional View of Planhard Carburetor Showing Fuel Supply Regulating Needle.

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 auxiliary 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.

[subsumed][merged small][graphic][subsumed][subsumed][merged small][merged small]

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?

A. The most common symptom denoting an excess of air is pop

« НазадПродовжити »