THE SPARKING PLUG.

Putaruru Press, Volume IV, Issue 152, 30 September 1926, Page 7

THE SPARKING PLUG.

— ■<&- With a modern engine run under proper conditions a well-made sparking plug should require no attention beyond an occasional examination for the purpose of adjusting the spark gap; yet from the number of plugs that we see badly sooted, we expect that many driver's have to clean their sparking plugs frequently, and we think in many cases much of this work could be avoided. In cases'where the plug is fouled with lubricating oil, the trouble may be due to worn ‘piston rings or cylinders, and the remedy then, of course, is difficult; but

re ii should he remembered that most of he the oil is sucked past the piston rings ‘ when the engine is throttled down, ■ especially when running' down hill | with the throttle closed and with the I engine being used as a brake. In the "majority of cases, however, it is found that sooting is due to running on too rich a mixture. When starting an engine from cold it is necessary to have a very rich mixture, but v as soon as the engine has started the strength of the mixture should be gradually weakened to the correct setting. Most cars are now provided with a mixture control lever, and the ! best setting of this lever, is at the " weakest position, with whidh the en- ; gine will give its full power. This is easily tested by running the car on a . level stretch of road, or preferably slightly up-hill, opening the hand throttle to a suitable fixed, position, and then gradually weakening the i mixture until a point is found where the power definitely begins to fall off. Just above this point is the correct running position. Carburettors are arranged so that they automatically , adjust themselves to the various enm gine speeds, but actually when runr.ing for any length of time at low

speeds—say, below 15 miles an hour -—it is usually found better to increase the strength of the mixture slightly. If the engine is run on too weak a mixture the effect is to heat the engine rapidly, owing to the fact that the gas mixture is so diluted that it bums slowly in the start to give its full power. It is important, however, that new drivers should give some careful attention to this matter of the correct mixture. If by mistake the engine has been rushed a considerable time on too rich a mixture, but before actual misfiring has occurred, much of the soot can be burnt away by running the engine under load on what is normally too weak a mixtureThis will have the effect of heating the engine, and so it should not be carried too far;, but it will clear all the soot off the sparking plug insulation. By understanding the effect of changes in the mixture control most of the misfiring and plug cleaning should be avoided.