LOSS OF POWER.

King Country Chronicle, Volume XXV, Issue 3278, 12 March 1931, Page 2

LOSS OF POWER.

Motorists will be surprised to learn that it is computed that about one car in every five loses engine efficiency in some degree owing to petrol gas forming in the fuel line. The cause of this trouble is usually owing to the petrol lead running too close to the exhaust pipe, or the carburettor, or the vacuum tank is overheated owing to high temperature under the bonnet; this has a tendency to boil petrol and the resulting gas forms into bubbles that interrupt the even flow of petrol. This causes the engine to lose power, misfire, and even sometimes to stop entirely owing to fuel starvation. It will surprise many car owners to learn that at about 90 degrees atmospheric temperature, the heat under the bonnet may climb as high as 230 degrees, whilst the temperature of the carburettor jet may reach 175 degrees. This “jet” figure—the Dunlop Company states —was ascertained during recent tests at the University of Michigan, U.S.A., where a carburettor made of glass was tested for petrol bubbles, under varying degrees of heat. In the test it was found that the petrol bubbles, at high engine speed, were sucked through the jet with little effect on engine running, but once the revs, got down the bubbles increased in size and choked the small orifice or jet. When it is pointed out that the volume of petrol gas is approximately 185 times greater than an equal weight of liquid petrol, it will be realised how impossible it is for the very small hole through the carburettor jet to pass sufficient gas to enable the engine to function properly. This explanation will probably elucidate for many motorists why their cars run so much better and smoother during cool weather, than when the thermometer figures register high. To cure the trouble cited is in some cases a difficult matter, but where it is found that the petrol lead runs close to the exhaust pipe or near the exhaust box, and gets unduly hot, this can be remedied by lagging the exhaust pipe with asbestos cord, or by removing the petrol pipe to the opposite side of the chassis. A cure has been efl'ected in some instances by fitting a larger petrol pipe, and covering the vacuum tank with asbestos sheeting. A change of petrol will sometimes overcome the trouble, for the more volatile the fuel is, the readier it will form gas under healed conditions in the petrol lead. A heavier grade fuel may therefore improve matters, although it may slightly affect the starting of the engine, but that trouble does not often worry motorists during the summer months. ENGINE STARTING. Difficult engine starting can some-' times be traced to a weak magneto, the current generated being unable

to produce sufficiently vigorous sparks at the plug points. Decreasing the plug gap may help matters, but it is claimed that in an emergency a start can be obtained if the plug points are liberally coated with graphite by being rubbed with a lead pencil. This is said to decrease the resistance offered by the plugs, thus enabling a reasonably intense spark to jump the points. So soon as the engine starts it will generally be found that if it is kept reviving the weak magneto will function moderately well. It should, of course, be repaired as soon as possible.