In some types of Schebler carburetors, the float chamber =B= is surrounded by a water jacket that is supplied with hot water from the cylinder jackets of the engine. This keeps the gasoline warm so that it evaporates readily under any atmospheric conditions. The quantity of air admitted to the carburetor is controlled by an air valve shown in the air intake by the dotted lines. This is adjusted by hand for a particular engine and is seldom touched afterward. When starting the engine it is necessary to have a very rich mixture for the first few revolutions, this mixture being obtained by “flooding” the carburetor. On the Schebler carburetor the mixing chamber is flooded by depressing the “tickler” or flushing pin =V=. (107) Two Cycle Carburetors. Nearly any type of carburetor can be used on a two port, two stroke, cycle engine providing a check valve is placed between the crank case and carburetor to prevent the crank-case compression from forcing its contents back through the inlet passages. A great many manufacturers make special carburetors for two stroke motors that have the check valve built into the carburetor itself. With three port two stroke cycle engines a check valve is not necessary as the piston in this type of engine performs this duty. In that class of vaporizers known as mixing valves, the valve that controls the flow of gasoline blocks the air passage in such a way that an additional check valve is not necessary. (108) Kingston Carburetors. The Kingston Carburetor shown by Fig. 117 differs from the Schebler in many details, the principal difference being in the construction of the spray nozzle and the construction of the auxiliary air valve. The throttle valve E controls the exit of the mixture through the engine connection C which is an extension of the mixing chamber. The spray nozzle J which is surrounded by a hood or tube is controlled by the needle valve A which is threaded into the top of the mixing chamber, this latter adjustment being locked into place by a button head screw and a slot in the casting. [Illustration: Fig. 117. Cross-Section Through Kingston Carburetor Showing Balls Used for Auxiliary Air Valves. ] Surrounding the nozzle tube or hood is a curved restriction in the air intake passage, is known as a Venturi tube, which insures a constant relation between the air and fuel supplies. As the action of the Venturi tube is rather complicated, it will not be taken up in detail. Air is supplied to the Venturi passage through the intake (D). An annular float (K) surrounds the mixing chamber that acts on the gasoline supply valve (I) through a short lever arm. This valve is accessible for cleaning on the removal of the cap H that covers the valve chamber. Gasoline enters the float chamber through the fuel pipe G, and enters the spray nozzle through the two ports in the base of the mixing chamber.