Page:Motors and motor-driving (1902).djvu/198

166 (b) Too rich a mixture may be caused by the presence of too much petrol in the carburator; if this is so, turn off the petrol supply for a time and revolve the engine again with all air inlets wide open until the first explosions are obtained.

(c) Perhaps the cylinder cannot get any petrol vapour, owing to the nipple (in a float and jet type carburator) being stopped up. This nipple can be taken out with a special key and cleaned by passing a fine needle through it, taking great care not to enlarge the hole in the least degree. Possibly there is no petrol in the tank, or you have forgotten to turn it on, or the tank is almost empty and the car tilted by standing at the side of the road; push it over to the other side. One can tell if there is any petrol in the carburator by the position of the float needle, and the novice should provide himself with a diagram of his carburator.

(d) In cold weather, if the car has been standing idle for some time, considerable difficulty may be experienced in starting up. Petroleum spirit will of course vaporise far less readily at a low temperature than at a high one. Artificial heat is therefore the remedy, and this can be most easily applied by taking out the mushroom-piece in the carburator (if there is one), and warming it over the burners or otherwise; or warm petrol may be squirted into the cylinder or induction pipe or valve. In obstinate cases it may be necessary to warm the carburator underneath by means of a little cotton waste soaked with methylated spirit. There may be a slight flare up, but this will assist the carburation, and there is nothing to fear from it so long as the main supply cock has been carefully closed.

(e) Stale Petrol.—The petrol remaining in the carburator may lose its strength if the car has been standing a long while; it should be emptied out and refilled: A good plan when about to put away the car for some time is to stop the motor by turning off the main cock, so letting it use up the last drop of petrol in the carburator.

The petrol in the main tank may also become heavy in course of time, especially if free access of air is allowed to it. A small instrument called a densitometer is sold for determining the specific gravity of petrol; the best specific gravity for starting is ·680; if your petrol when tested shows heavier than sp. gr. ·700 it should be changed or the tank shaken up.

(f) Perhaps there is nothing wrong after all, except that you do not turn the starting handle fast enough to cause vaporisation. Remember that a few smart turns with the whole of your energy