The pipe by which the gasoline flows from the tank to the carburetor should project slightly above the bottom of the tank, to prevent sediment from being drawn into it.
As gasoline rots rubber rapidly, hose should never be used to conduct it, nor should joints be packed with rubber. Copper and brass are attacked by gasoline less than other metals, and should always be used in preference to iron, which is corroded by the liquid. Joints may be made tight by the use of shellac or soap.
THE CARBURETOR
Besides the possibility of getting out of adjustment, the greatest trouble with a carburetor comes from the clogging of the passages and openings with dirt. When dirt enters, it clogs the gasoline inlet valve and prevents it from seating properly, the float chamber being flooded as a result. When the level in the float chamber is raised, more than the required amount of gasoline flows out of the spray nozzle, and the mixture that is produced is too rich. This will also result from the bending of the valve stem or the wearing of the seat, either of which will prevent the proper shutting-off of the flow when the correct level in the float is reached.
A flooding float chamber may also be caused by a float that is out of adjustment on its stem or too heavy. In the course of time the gasoline will cut a hole through the metal of a float and leak in, and leakage will also occur if the soldered joints open, the float then becoming too heavy and not closing the gasoline inlet valve at the correct time. These holes will be too small to permit the gasoline to be poured out, but by placing the float in hot water, the gasoline will be evaporated and driven out as a gas. In repairing a float, as little solder as possible should be used in order that the weight of the float may not be greatly altered. A cork float will become soggy and heavy if the varnish coating is damaged and the gasoline soaks in.
Carburetors are built so that the float valve and spray nozzle may be easily cleaned, for by withdrawing plugs fine wire may be run through them. When a carburetor is taken apart for more thorough cleaning, the position of the gasoline and air adjustments should be remembered, in order that they may be replaced in approximately the correct positions, thus saving time in making the adjustments that will be necessary.
The main air intake should be kept clean, especially when it is covered with a wire gauze screen. Dirt will reduce the size of the opening, and the air that enters will not be sufficient to give a mixture of the correct proportion. The screen should be kept clean and free from oil, for the latter is a dust collector.
COMPRESSION TROUBLES
A leak in the combustion space will reduce the compression by permitting the fresh mixture to escape during the compression stroke, and will also give an escape for the pressure resulting from the combustion, the pressure on the piston being reduced in consequence. The most frequent cause of leakage is worn valves, the intense heat tending to warp the disks and to roughen their surfaces, the exhaust valve being especially liable to this as it is surrounded by the hot gases during the time that it is open. A badly fitting spark plug, igniter stem, relief cock, or other opening into the combustion space will produce the same result. Whenever possible, these parts should be fitted with copper asbestos washers, which are soft enough to squeeze into the inequalities of the surface, at the same time resisting the heat and pressure.
When piston rings or cylinder walls are cut or scratched by running without oil, the pressure will escape into the crank case, which, while warm when the engine is running properly, will be heated to a very noticeable degree under these circumstances. The only remedy is the use of new piston rings and the reboring of the cylinder. Piston rings, being of cast iron, are brittle, and must be handled carefully. To place them in position in their grooves, thin strips of steel, like pieces of a hack-saw blade, should be bound to the piston, covering all but the lower groove. The ring for this groove can then be slipped on, and when it is in position the steel strips moved upward to expose the upper grooves, one at a time.