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.

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

Fig. 72.-Outlining Method of Utilizing Water Spray in Kerosene Vaporizer to Facilitate Combustion.

ping back in the carburetor, and loss of engine power even if there 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 gas burner of the Bunsen type or blue flame oil burner.

Q. What color is the exhaust flame when there is too much gasoline?

A. If the exhaust gases are reddish in color, it indicates a surplus of fuel.

Q. What color is the exhaust when there is too much air in the mixture?

A. The exhaust flame is yellow in color when there is an insufficient amount of gasoline in the mixture.

Q. What is the advantage of water-jacketing a carburetor?

A. It is very desirable to water jacket the float bowl of the carburetor and the mixing chamber and to pass some of the cooling water from the cylinders through this jacket. The heat assists in vaporizing the liquid and makes more uniform mixture proportions.

Q. Why is it desirable to supply hot air to a mixture?

A. In many cases the main air supply is taken from a point near the exhaust manifold so that only heated air is drawn into the carburetor. The advantage of using heated air is that it is more suitable for use with low grade fuels which do not evaporate readily than cold air. The warm air tends to vaporize the liquid, whereas cold air tends to condense the vapor.

Q. How are low grade fuels utilized with conventional vaporizers?

A. There are two methods of using carburetors of the design adapted for gasoline with the lower grade fuels such as kerosene. These are outlined at Figs. 72 and 73. In the former, in addition to pre-heating the fuel by a water jacket around the float bowl, a spray of water is injected into each gas charge. The function of the liquid is to turn into steam from the heat of the explosion, liberating oxygen which combines with the surplus carbon and tends to make combustion more perfect.

At Fig. 73, a carburetor intended for use with either kerosene or gasoline is shown. The supply pipes from both gasoline and kerosene tanks are led to a common fitting or valve which can be turned so that either liquid will be supplied the float chamber. When gasoline is used, the mixture flows directly to the cylinder because the supplementary throttle is moved in such a position that the

mixture is not forced through the fuel gas vaporizing coil, but passes right into the cylinder through the main throttle and gas outlet. When kerosene is employed, however, it is necessary to heat the vapor to insure thorough vaporization. The supplementary throttle is then moved out in such a way that the fuel gas must pass through the vaporizing coils which are surrounded by the hot exhaust gases before they are drawn into the cylinders.