This carburetor is started on gasoline. When the engine is hot, a switch valve is operated to permit the burned gases from the engine to flow through the carburetor; they pass through the pipe C, D, and as the chamber G is directly in their path it becomes intensely heated. The carburetor can then be switched to kerosene. A side view of this carburetor is shown in Figure 27. These carburetors are all of the float feed type, and are used on engines of which the speed is variable. A carburetor that is fed by a pump is shown in Figure 28. This is a simple tube with a fuel cup cast on one side of it. Fuel is pumped to the bowl, and the proper level is maintained by an overflow through which excess fuel passes back to the tank. This carburetor is intended for an engine of which the speed does not change greatly. Its only adjustment is the spray nozzle, and this is altered to correspond with changes in engine speed. [Illustration: FIG. 27.—“E-B” CARBURETOR, SIDE VIEW] [Illustration: FIG. 28.—PUMP-FED CARBURETOR] If an engine is clean and in good condition, it will run as well on kerosene as on gasoline, although the heating effect of kerosene is greater. When an engine is carbonized, as is usually the case, a condition known as _preignition_ will occur unless it is prevented. Carbon from unburned fuel or from lubricating oil will deposit on the piston head and the parts of the combustion chamber, and particles will become heated to the glowing point, when they will set fire to the fresh mixture during the compression stroke and before the proper time. The effect is to make the engine lose power, and it also gives rise to a sharp metallic knocking. By reducing the temperature in the cylinder during the compression stroke this condition can be prevented. This can be done by adding water vapor to the mixture, and kerosene carburetors are therefore built with a water attachment. As can be seen in Figure 28, this is a water cup and spray nozzle like those for the fuel. When the engine knocks, and shows that preignition is occurring, water is turned on, and, being carried into the cylinder, keeps the mixture from being heated to the point of ignition before the proper time. Figure 29 shows the attachment of this carburetor to an engine which, in this case, is horizontal. To start the engine, gasoline is injected into the carburetor, as shown; this will give a sufficiently good mixture for the purpose, and enough heat for running on kerosene is thus obtained. [Illustration: FIG. 29.—“TITAN” CARBURETOR] [Illustration: FIG. 30.—PUMP-FED CARBURETOR WITH TWO FUEL NOZZLES] The carburetor shown in Figure 30 is similar, but has a bowl and spray nozzle for gasoline, to use in starting. It is also provided with a heating jacket through which hot water or hot gases may circulate.