All About Engines

The Petrol Motor 221 the action of gravity. The carburettor is fixed in such a position that the supply of oil to the jet is not affected by the inclination of the jet when going up hill, but it does not differ in construction or principle from those used on other types of petrol engine. Similarly the explosive mixture is fired by a spark from either a coil or a magneto, the latter being, perhaps, more frequently fitted. Figs. 125 and 126 on Plate 21 show a 3|-horse- power Humber and a 6-horse-power V-type A.J.S. engine. Engines for Motor-boats The earliest internal combustion engines used on boats were simply motor-car engines—extremely light, quick-running engines which gave wonderful speeds and led to a great development of racing. For most purposes, however, a heavier, slow-speed engine is to be preferred, and during the last fifteen years engines have been specially designed for the purpose. As these were less economical, there has also been a tendency to use paraffin instead of petrol. The typical motor-boat engine of to-day is, therefore, a small marine engine, using paraffin as fuel, strongly built, and running at a moderate speed. Generally, the cylinders are in a row, because this arrangement takes up the least space transversely, and if the V form is adopted the angle between each cylinder of a pair is, for the same reason, a very small one. The chief disadvantage that attends the use of