In addition to the flush pin found on carburetors, many are provided with other devices to render starting easy. It is well known that a "high-test" gasoline, such as a 76, will vaporize more easily than will one of a lower degree of specific gravity. Also, every motorist has had impressed upon him the fact that heat aids in the vaporization of gasoline. If we try to start a motor on a cold morning with a low-grade gasoline, such as the 60- or 62-degree fuel now generally obtained, we know that a rag dipped in hot water and wound around the carburetor will help matters.
To enable low grades of fuel to be properly vaporized under all running conditions, many carburetors are provided with a water jacket surrounding the vaporizing chamber. This jacket is connected with the cooling system of the motor, and the hot water surrounding the chamber so warms the interior that vaporization is greatly facilitated. Some of these systems are provided with a shut-off cock by means of which the carburetor may be operated with hot water in the jackets, or not, as desired.
Other carburetors employ a jacket surrounding the exhaust pipe of the motor and connected with the vaporizing chamber. The air is heated by the hot exhaust pipe as it is sucked into the carburetor, and this also facilitates the vaporization of the fuel. Some carburetors are provided with both jacket systems, while others have neither, but whatever design is installed, the best results will be obtained if cold air is used after the motor is once started. Cold air is more "concentrated" and contains a greater amount of oxygen per cubic foot than does air that has been expanded by heat, and consequently many carburetors are provided with a means of turning off the hot air after the motor is started.
The higher the degree of specific gravity of a fuel on the Baumè scale, the more volatile will it be, and consequently a 68° gasoline will vaporize more easily and give more power than will a 60° or 62° fuel. 72° gasoline is often used in races, but the average motorist does not get better than 64°—and he is sometimes lucky to obtain fuel of that specific gravity. A hydrometer, or specific gravity tester, is a convenient instrument for the average motorist to own, and with it he may tell exactly what grade of fuel he is paying for. The Baumè scale, by which all gasoline is tested, reads in degrees, and the specific gravity is obtained by observing the depth to which the hydrometer sinks in the liquid. This instrument resembles somewhat a glass thermometer, and is so graduated that the deeper it sinks in a liquid, the higher will be the reading on its scale.
Water in the fuel is an annoyance that is often encountered by the automobilist and the motor boatman, and this will make its presence known by causing the motor to skip when all adjustments and connections seem to be in perfect condition. Water is much heavier than gasoline and has no affinity for it, and consequently, as it sinks to the bottom of the tank, a few drops in a large amount of gasoline will cause trouble by passing out through the needle valve at intermittent intervals and forming an unexplosive mixture.
The presence of the water in the fuel may be detected easily without the use of a hydrometer by drawing some gasoline from the bottom of the tank into a tin or white-enameled cup. If water is present, it may be seen in the form of small globules in the bottom of the cup. If the contents of the cup are poured over a flat surface so that the liquid may be allowed to spread, the gasoline will be seen to cover a large surface and evaporate quickly, while the water will seem to remain in the globules unevaporated for some time after the gasoline has disappeared. This latter test will sometimes show the presence of water when none can be discerned in the bottom of the cup before the contents are poured out on the flat surface.
The practice of "doping" the fuel tank by adding to the gasoline ether or some other highly volatile liquid is not to be recommended to the average motorist. A few ounces of ether or chloroform added to the fuel will form a more volatile and consequently more powerful mixture, but unless the greatest care is taken, the motor is liable to be completely ruined by such a procedure. Numerous cases are on record in which cylinder heads have been blown off or castings cracked by the force of some of the explosions when too much "dope" has found its way into the mixture.
Although the average motor gasoline obtainable nowadays is hardly all that could be desired as automobile fuel, a little care taken when filling the tank will eliminate many of the carburetor annoyances to which many cars seem to be subject. The cap of the tank should never be taken off when the air is filled with particles of dust that are liable to find their way into the fuel, and care should be taken to see that no pieces of the rubber or leather washer or packing drop into the gasoline when the cap is removed. Foreign matter and water that may be in the gasoline when purchased may be removed by straining the fuel through a chamois skin placed inside of the funnel through which the tank is filled.