PETROL CONSUMPTION

New Zealand Herald, Volume LXXIII, Issue 22444, 13 June 1936, Page 11 (Supplement)

PETROL CONSUMPTION

DRIVERS' COMPLAINTS A BAFFLING PROBLEM One of the most baffling problems in motoring is that relating to petrol consumption. Purchasers of cars are frequently heard to complain that tho mileage per gallon is not what it was guaranteed to be, this applying to new as well as second-hand vehicles. In the case of now cars the petrol consumption should bo at least what is claimed for it by the makers, and in most instances it will be found so. provided tho oar is driven in a reasonable manner and kept in clean, working order. It should be recognised that petrol consumption may be largely influenced bv the driver. The motorist who constantly drives at high speed, accelerates rapidly and uses his brakes unnecessarily, uses more petrol than the careful driver who avoids such practices. It must be realised, 100, that petrol eonsuption is heavier on vehicles when they are used for broken journeys, which involve frequent stops. With regard to used cars, there may he many reasons for petrol consumption being higher than it should be. If tho consumption is believed to be excessive a search for the cause shoujd he made. A British motor engineer, writing in Motor Transport recently, pointed out that if the petrol was to be used to full advantage there must be no leakage; all petrol must be efficiently vapourised and the charge ot petrol vapour and air must he efficiently tired and exploded at the right moment. Evidently the first thing which suggests itself is a close examination of the petrol supply pipe and its unions for signs of leakage. Trouble may be caused by flooding of the carburetter. A defective needle valve or a punctured float may be responsible for serious waste. Too large a jet sometimes is the cause of the trouble. The host results are obtained with the smallest jet that will givo satisfactory running. JI the charge of petrol vapour and air is not efficiently fired and exploded there will he loss of power, which means reduced'mileage per gallon. For the charge to he efficiently tired and exploded there must be good compression and a Hat spark produced at the right instant.

If the spark is not good it may be due to dirtj' plugs or to some fault with the ignition system. Often the cause is too wide a gap between the points oi the sparking plug. Correct ignition and valve timing is essential for satisfactory running, and running with retarted ignition is a common cause of high consumption, for then the explosions occur too late to produce the full effect. Valves must not only bo correctly timed, but they must have the right amount of lift and they must be gastight. Frequently, through being scored and pitted, they allow gas to escape when down 011 their seatings, but a much more serious escape of gas occurs if owing to wrongly adjusted tappets, they do not close properly. This escape of gas leads to high petrof consumption. Leakage past the pistons will also produce the same results. 111 several ways, too, carbon deposits about the cylinder heads, pistons and valves may lead to loss of power and waste of fuel.