The almost universal method of starting the motor is by means of a handle whereby the piston is operated and the charge drawn into the combustion chamber. In the case of cars with two or more cylinders various self-starters have also been introduced, which, on touching a button, explode the charge which remains in one or other of the combustion chambers, and so start the engine. These appliances, however, are only effective for a few hours after the engine has been running, as the charge escapes gradually.

There are various types of petrol engines on the market, but the main principles remain the same in all. The vertical engine is the most popular; then comes the horizontal, and in other cases engines worked at varying angles. Once, however, the motorist has thoroughly grasped the principle of the petrol engine, there is little difficulty in understanding these varieties. The same series of operations take place in the small single-cylinder engine of the motor-bicycle as in each of the four cylinders of the 60 h.-p. racing car.