Vaporizing The Fuel

There are in general use two devices for mixing the gasoline and air to form the vapor. These are the vaporizer and the carburetor. The vaporizer is a device that mixes the gasoline and air by the operation of the motor, that is, the up stroke of the piston acts as a pump and draws in the supply of air. This mixes with a jet of gasoline and passes into the base. The down stroke of the piston compresses this vapor so that when the port opens it passes into the firing chamber above the piston.

The gasoline feed of the vaporizer is regulated by a needle valve, and the air supply is usually taken through a cheek valve. The vaporizer mixes sufficient vapor at each cycle for the charge only.

The carburetor produces the vapor by bringing a quantity of air and gasoline into contact, either by drawing the air through a reservoir of gasoline or over its surface. The carburetor has a supply of vapor in reserve. Both the vaporizer and carburetor operate better in warm than in cold weather, as the expansion of the gasoline greatly reduces the temperature. This is overcome by heating the air supply. A simple heating device is to place a perforated collar over the exhaust pipe, thus making a hot air chamber and connecting this with suitable piping to the intake air valve.

Control

As the marine motors are all comparatively high speed, the piston travel is very quick, and in order that the thrust may be given to the piston the ignition must take place at such a point as gives the best results. Regarding this we must consider two points-the speed of the piston and the time required to expand the charge after it has been ignited. We will make this point clear, as it is of importance to the amateur operator. In the first place, the sparking device on all motors is or should be regulated by a lever under the operator's control so that by manipulation of this lever the spark (time of ignition) may be advanced so as to cause early ignition, or retarded so as to cause late ignition at will. Now supposing the motor is turning very slowly (as when cranking it ) the lever should be set 60 as to fire the charge just when the piston is starting on tha down stroke. But as the speed of the motor increases the travel of the piston becomes so fast that it does not receive the impulse, that is, the charge has not had time to fully expand while the piston is on the downward stroke, therefore the time of ignition must be advanced to that point which will give the greatest force of the expansion to the down stroke of the piston. This results in the ignition taking place while the piston is on the up stroke; that is, while it is still compressing the charge.

The regulation of this is a very simple matter and is, of course, dependent upon the speed or number of revolutions the motor is making. The operator merely manipulates the controling lever.

By advancing it he will increase the speed up to the maximum point. By retarding it he will decrease the speed or check down the motor.

It is by this manipulation of the spark that the motors may be made to run either way. After one becomes thoroughly familiar with some of the smaller two cycle motors, they can be slowed down and reversed without stopping, through a proper manipulation of the spark control.

When the motor is to be run under check for any length of time, the supply of vapor must also be reduced.