MIXTURE CONTROL

Nelson Evening Mail, Volume LXVI, 18 June 1932, Page 3

MIXTURE CONTROL

PROPER USE ESSENTIAL Few drivers realise the amount of damage which is done to cylinders and sparking plugs by the misuse of f lic mixture control. The only reason for the existence of this control is to get a temporarily rich mixture for starting while the cylinder block and ignition pipe arc still cold. Once the engine has started the control should be moved to weak as soon.as the engi no is warm. It has been ascertained that cylinder wear amounts to as much as onethousandth of an inch in every thousand miles driven when the mixture control is abused. As the clearance between the piston and cylinder wall originally' allowed by IJhe makers is in the region of only four-thousandths ot

I an inch, this clearance may very easily, bo trebled in less than one season’s running, and then oiling up of plugs, due to liquid oil passing into tho combustion chamber, will be a probablo result. , Incidentally, when this happens tlie insulation of the plug, if made of mica, should not be cleaned with an abrasive material. The most desirable state lor a mica plug is with the highest possible polish on the mica. In cases where the mica is corrugated to give greater resistance to soot and oil the edges of the corrugations are. of course, sensitive, and should be treated with great respect. The only really safe way of cleaning a mica-insulated plug is with a soft rag dipped in petrol. If the insulated centre is in a particularly bad state it should be steeped in petrol for an hour or two and then dried thoroughly before attempting to clean it.