The gasoline pump is of the ordinary plunger kind, like those used for pumping water, and it is worked by an eccentric on the camshaft, as shown at B. The piston rod of the pump has a handle attached to it, so that enough gasoline to start the engine can be pumped by hand should it be needed. The pump draws the gasoline from the bottom of the supply tank into an overflow cup, that is, a small FIG. 38-B. PLUNGER PUMP FOR THE PUMP FEED SYSTEM vessel which holds about 1/2 a pint of gasoline and sets above the engine. The excess gasoline that is pumped into the overflow cup runs back to the tank through a return pipe. The gasoline flows by gravity from the inside of the overflow cup to the gasoline valve. The Gasoline Valve.-Numberless schemes have been devised to break up the gasoline into a spray and mix it with the right amount of air to make the fuel mixture. For a stationary gasoline engine a very simple and satisfactory device for this purpose is to use a needle valve and set it into the casing of the fuel inlet valve just back of the valve head, as shown in Fig. 39. A needle valve is merely a small tube one end of which is formed into a nozzle with a little hole in it. A small rod, or needle, with a tapering point, sets in the tube and can be adjusted so that the NEEDLE INLET FOR NEEDLE VALVE POPPET VALVE FIG. 39. THE GASOLINE VALVE amount of gasoline flowing through the nozzle can be varied. The end of the needle valve tube that projects outside of the cylinder is connected to the overflow cup by a length of pipe. The way the gasoline valve works is like this: when the fuel inlet valve opens the suction stroke draws the gasoline from the overflow cup through the gasoline valve into the cvlinder in a spray. The minute particles are vaporized by the heat when they readily mix with the air which is taken in by the air valve at the same time. As the fuel inlet valve is controlled by the governor in the same way as the gas inlet valve on a gas engine, just enough gasoline is taken into the cylinder to drive the engine under all conditions of load, be it light or heavy. CHAPTER V MOBILE GASOLINE ENGINES Mobile gasoline engines are those made small, light and strong enough so that they can be used to power motorcycles, motor cars, motor boats and airplanes and drive these various vehicles over land, water or through the air. While these mobile engines work on the same general principle as stationary gasoline engines, yet they differ greatly in detail and each type must be designed for the special work it has to do. PART I THE MOTORCYCLE GASOLINE ENGINE All motorcycle engines are built on the four stroke cycle principle, and they are made with one, two, four and eight cylinders.1 The one and four cylinder engines are of the vertical type and the two and the eight cylinder engines are of the V type, as shown in Fig. 40. The Fuel Supply System.-The gasoline system or fuel system, as it is called, consists of two chief parts, and these are (1) the tank, which contains the supply of gasoline, and (2) the carburetor, which regulates the amount of gasoline used, breaks it up into a spray as it is needed and mixes it with air to make the fuel mixture. The Gasoline Supply Tank.-In motorcycles the tank is always set above the engine and the gasoline is fed into the carburetor by gravity. Why a Carburetor is Used.-Instead of the simple gasoline valve which is used on stationary engines, all mobile gasoline engines employ a more 1 The eight cylinder motorcycle was a racing machine built by the Curtiss, Co., of Buffalo, N. Y. |