TESTING SPARK PLUGS.

Putaruru Press, Volume VIII, Issue 364, 13 November 1930, Page 7

TESTING SPARK PLUGS.

The plug should be so placed that the points are visible when cranking the engine. Next turn the engine over a few times (at least as many times as there are cylinders), and note whether a spark jumps across the air-gap between the points. It is not sufficient, however, merely to ascertain if there is a spark, but to note as well if it is hot enough to fire the charge of compressed gas in the cylinder. This is often difficult, but usually, if the spark is a heavy blue, a bluish-white, or a “ fat ” yellow one, it is probably satisfactory. If it is very thin and greenish, or showing red, it is more than likely too weak. Some idea of the appearance of a good spark can be obtained from the ; following procedure: With the en- j gine in a satisfactory running condi- . tion, loosen the nut on top of one j plug. Then start the engine, and, by taking hold of the insulated part of the high-tension current lead, move the end [very slowly away from the spark plug terminal, and watch the • spark jump, noting carefully both its | colour and volume. Observe also the distance the spark jumps; but be i careful not to force it to jump too I great a gap, or hold it in such a position that the spark cannot jump to the plug or the engine while the motor is running, since this tends to break down the insulation of the coil.