THE SPARKING PLUGS

It seems logical to deal first with these very important items and then work back through the other components in the ignition system in the order in which the work is likely to be tackled by the average owner.
The rules for sparking plug efficiency can be summed up briefly: fit the correct grade of plugs; service them at regular intervals—at least every 6,000 miles, and more frequently if the engine is no longer in first-class condition—and renew them while they still have a reasonable remaining lease of life. Keeping plugs in use until they are completely worn out is an expensive form of economy.

When plug trouble does develop, try to arrive at the basic cause before blaming the plugs themselves. Retarded ignition timing, overheating, excessive oil consumption or a weak carburettor mixture are some of the factors that can affect plug performance.