MOTORING
The Petrol Ration AN allowance of about zoo miles in every month for private cars is very short commons—so short, in fact, that I imagine the ration to which we are from now on limited will eventually be extended. A considerable number of the public will have to use their cars regularly on the business which the Govern- ment urge us to keep going, and as for most of them fifty miles a week cannot be enough, it is obvious that the strictest economy must be practised and every known dodge adopted to make the allowance go as far as possible. The first thing to do is to put the engine into its best condition, inefficiency being one of the main sources of waste of fuel. Sparking plugs should be taken out, cleaned and have their gaps adjusted correctly. If you can afford it, buy new ones—the simplest way of giving new energy to an engine and saving petrol. The distributor should be thoroughly overhauled for lurking dirt and the contacts touched up. The exterior of the plugs themselves, as well as all connexions, must be kept free of oil-and-dust film, which, by interfering with the insulation, however slightly, tends to reduce the spark-intensity, as well as making starting less ready and thereby wasting petrol.
Do not attempt to economise petrol by admitting more air to the carburettor either by reducing the jet-size or by any other means. The most economical mixture in driving is as a rule the most efficient, and you can take it for granted that both these aims have been very carefully pursued by the makers of the car before it was put on the market. There may be exceptions to this rule in the case of high-speed cars of the sports type, but not in the normal family models. Be careful to check the existence of leaks in either petrol-pipes or inlet washers. Anything that obstructs the free flow of petrol to the float-chamber or jets causes waste, because it means you have to open the throttle wider and drive the engine harder. Keep the carburettor absolutely clean. I don't know what the War-petrol will be like, but it is wise to guard against the chance of dirt in it. The smallest, almost invisible, obstruction has its effect on consumption, even though the performance of the engine is not seriously impaired.
Find out as soon as possible what is the economic speed of your car. Like a ship, every car has an unvarying speed at which it runs efficiently—that is, at a useful pace—on its minimum amount of fuel. Sometimes this speed is low, 20 miles an hour, but more often it is between 30 and 40. Take a familiar stretch of road and check the consumption very carefully, noting all conditions, surface, wind, rain, gradients, and so on, trying out a different cruising speed each time you go out on it—say, 25, 30 and 35 or 40. It is astonishing how much normal consumption can be reduced by -sticking to the economic speed as much as possible. In my own experience I have raised the m.p.g. from 23 to 27 in a car by keeping the speed-indicator at 40 m.p.h., neither more nor less, whenever circumstances permitted.
Above all, avoid sharp acceleration, violent braking and con- stant fluctuation of pace. Whether you discover the economic speed or not, take great pains to drive as steadily as possible, and if you have hand-control to the throttle use it instead of your foot. An unvarying throttle opening means less fuel used than the " fluttering " one inevitable with foot-control, which can never be absolutely steady. With a hand-control you will generally find that you can gradually shut the throttle till the engine is running on no more than a whiff, without losing speed. It may well be worth while having a Bowden wire control fitted. I have never been able to prove that in ordinary driving on British roads coasting, the clutch out with the engine ticking over, makes any difference over the very short time this is possible, though, of course, regular switching off and coasting on long hills must have an effect in the long run. As one can seldom do this for more than a mile at a time on any long drive too much should not be expected from the practice. But it is worth trying.
For the rest, get going—gently, of course—the moment the engine is started ; switch off at every halt ; change gear as seldom as possible ; keep the throttle-opening small ; start and slow down as slowly as you can ; use upper cylinder lubricant regularly ; keep the valves in gas-tight condition.
JOHN PRIOLEAU.
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