The first step in adjusting a carburetor is to get the engine running. The needle valve should be closed, and then opened enough to give a mixture on which the engine will start; on many carburetors this will be about one and one half turns. The engine should then be _primed_; that is, a little gasoline should be put in the cylinder, which may be done with a squirt can. When the engine is running, and is well heated, the needle valve should be gradually closed until the engine begins to miss, and to send jets of flame out of the carburetor, or little explosions occur in the carburetor. These are signs of a thin mixture, and the needle valve should be gradually opened to make the mixture richer. The engine will run more steadily, and will pick up speed until the mixture becomes too rich, when it will choke and black smoke will come out of the exhaust. The positions of the needle valve for a mixture that is too thin and one that is too rich have thus been found, and it remains to set it at that point between at which the engine runs most steadily and at the best speed. With adjustable air valves it is usual to adjust for idling, that is, the slowest speed at which the engine will run steadily without load, and then to make any necessary additional adjustment for full speed and power. If a carburetor cannot be adjusted by following the usual methods, trouble may be looked for, and this may be in the carburetor itself, in the fuel supply, or in the intake manifold, taking for granted, of course, that the engine is in proper condition and that the ignition system is operating correctly. Dirt under the float valve will prevent the valve from seating, and the level in the float chamber will be too high, so that the mixture is too rich. Lifting the valve from its seat will let fuel rush through, and loose particles will thus be washed away. If dirt is ground into the valve and seat, or if these parts are worn, the valve must be reseated, which is done by turning the valve against its seat with light pressure, the end of the valve being gently tapped with a light hammer. Under no conditions use a grinding compound, for the particles would become imbedded in the soft metal and would ruin the valve. Other causes of flooding are a bent valve, the sticking of the float pivot, and the soaking of fuel into the cork float, which is thereby made too heavy to float properly. The remedy is to dry it, and then to give it three coats of shellac. A frequent cause of trouble is dirt in the pipe from the tank to the carburetor. While there may not be enough dirt to prevent the engine from running slowly, it is sufficient to prevent the flow of sufficient fuel for full power. A strainer is always provided, and this should be drained every day; if this is not done frequently, dirt will work its way through.