How To Drive A Motorcar
A Key To The Subtleties Of Motoring

HOW TO DRIVE A MOTORCAR On the other hand, too rich a. mixture is likely to soot up the plugs, leave a deposit on the piston heads and around the walls of the combustion chamber, and likewise on the valves, and thus in the course of time will adversely affect the running of the engine and tend to cause pre-ignition. Too rich a mixture can usually be detected by a pungent exhaust which has a sort of stupefying effect if inhaled much, whilst the exhaust gas is usually dark and smoky. People occasionally find that a carburetter which, say, on a warm day in the winter, is quite satisfactory is, a few days afterwards, when a very cold day comes along, nothing like so efficient. It must be remem- bered that there are two contributory causes for this. In the first place, there is a difference in the air itself, and in the second place the lower the temperature thé less viscous the fuel, and as there always exists a definite relationship between the viscosity of the fluid and the skin friction engendered, so the flow in the jet varies. Consequently, if there is a spell of really cold weather and one’s carburetter is of the automatic type it may be found necessary, in order to get good run- ning, to put in a slightly larger jet. The Use of the Throttle It would be a fairly safe criticism to state that, in the majority of cases, the throttle is used too harshly. Perhaps it is a matter where it is really not much use even advocating the invariable gentle treatment of the throttle, and, of course, through it the mechanism of the car. but at the same time one may safely plead for careful use of it, except where rapid acceleration is needed, for instance, in traffic. In other words, unless there is some specific reason for very sudden accelera- tion, depress the throttle pedal gradually, and let the car pick up its speed in an even manner, instead of in the quickest possible way. It is fairly obvious, with but little consideration, that to open the throttls to its maximum from its nearly- closed position, involves a sudden strain not only on the engine, but upon all the various transmission units 76