FUEL CONSUMPTION

Wairarapa Times-Age, 23 January 1939, Page 8

FUEL CONSUMPTION

AIDS TO GETTING BETTER RESULTS.

There are few motorists who do not lake a considerable interest in the fuel consumption of their cars. However, the factors which have a direct bearing on it are so numerous that it is next to impossible to lay down a correct figure for any given make of car.

The manner in which the vehicle is driven, the condition of the valves, the adjustment of the carburettor, the state of the sparking plugs, and the degree of friction existing in the running gear, all are responsible for a good or bad result. It has been proved possible to obtain without any coasting a figure of 30 miles a gallon from a six-cylinder car weighing about 30cwt simply by ensuring in the first place that the car is in as perfect mechanical condition as it is possible to make it in every respect, and then driving it so carefully, at comparatively low speeds, and with very gentle use of the accelerator, that the minimum possible amount of fuel is used. But driving a car in this manner is really hard work, and all the pleasure of motoring is lost. With the same car in the same condition, the average motorist will be doing quite well to obtain 20 m.p.g., which, if there is any norm, is about correct for this type of vehicle. To obtain reasonable figures, the motorist will need to make sure that mechanically the vehicle is in good condition, and then, with sane driving, he can forget the matter of consumption, in the happy knowledge that this cannot help but return a figure that is not excessive.

One important factor in fuel consumption is that of chassis friction, usually caused by brakes so badly adjusted that one or more sets of shoes bind on the brake drums. In any case of excessive consumption the freedom of the running gear should first be tested, particularly if the brakes have just received attention, by seeing how well the car will roll of its own volition on a slight down grade. If it is free - enough in this regard, then attention may be turned to the engine. It is useless tinkering with the carburettor unless one is very sure that the engine is reasonably free from carbon and that the valves are seating well, and that their tappets are properly adjusted. If 10,000 miles or more ■have been covered since they wei-e last attended to, then the best advice that can be offered is to pay for a “top” overhaul and not until then to worry about other adjustments. In logical order, the sparking plugs and the condition of the make and break-mechan-ism must be considered next . If sparking plugs have been in use for more than 10,000 miles, throw them away and fit new ones* but in any case, make sure their gaps are set correctly according to the manufacturer’s advice. And do not make the mistake of fitting plugs that are tod “cold.” The ideal to be aimed at is to fit plugs which will just stand the heat of the combustion chambers without burning, and no more.

The carburettor is the final thing to be considered, and, remembering that the main jets are fixed, there is little sense in altering their setting, if the car previously had returned a good consumption figure. The points Cd look for are an excessively rich mixture at the idling jet, a punctured float which, filling with petrol, will become too heavy and allow the carburettor to flood, and a too-fast idling speed re--justment.

If all these adjustments have been made correctly and the consumption is still too heavy, then it is obvious that fuel is escaping somewhere, and the only logical conclusion is that the main fuel tank is punctured, or that there is a leak from the petrol lines.