BAD RUNNING

Evening Post, Volume CX, Issue 112, 8 November 1930, Page 24

BAD RUNNING

' ONE OF THE CAUSES It lias been computed that about one car in every five loses engine efficiency in some degree owing to petrol vapour forming in the fuel line. The cause of this trouble is usually owing to the petrol lead running too closo to the exhaust pipe, or the carburettor, or the vacuum tank ia 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 owing to fuel starvation. 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 figure was ascertained during recent tests at .the University of Michigan, where a carburettor made of glass was tested for i petrol bubbles, under varying degrees of heat. In the tests it was found that the petrol bubbles, at high engine speed, were sucked through the jet with little effect on engine running, hut once the revolutions got down the bubbles increased in size, and choked the small orifice of the 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 vapour to enable the engine to function properly. This explanation will probably reveal to many motorists why their cars run much better and smoother in cool weather than when the thermometer is high. To euro the trouble is in some cases a. difficult matter, but where it is found that the petrol lead runs dose