Candles change quite often, so naming a specific type of candle is impractical. When purchasing new candles, it is better to be guided by the data in the latest catalogs. The gap between the electrodes of the candle is 0.8 mm.
After 10,000 km of run, the spark plugs must be cleaned with a strong jet of sand and the gap between the electrodes adjusted. The gap is adjusted by pulling the side electrode. Exposure to the central electrode is not allowed, because. this may damage the insulator.
Before turning out the candles, check that there are no foreign objects in the recesses of the candle holes. Washers, bolts, pebbles or other objects falling into the spark plug hole after they have been removed can lead to damage to the valves, valve seats or cylinder head after starting the engine.
By the appearance of the candles, you can assess their condition and operation, as well as adjusting the carburetor, adjusting the fuel injection system, the composition of the fuel mixture and the condition of the engine (pistons, piston rings, etc.). The following is a description of the appearance of spark plugs and possible engine malfunctions:
Normal condition of spark plugs
The color of the insulator is yellow-brown to brown, most often with a powdery coating. The electrodes, in addition to soot, are covered with a powdery coating of brown-yellow or brown color. The inner surface of the candle body is light brown, yellowish or black-brown. The engine is correct. The spark plugs are correct.
Candles are smoked
The insulator, electrodes and the inner surface of the case are covered with a thick, powdery black-brown velvet coating. Causes may be a rich mixture (lack of air), prolonged operation of the starting damper, increased gap between the electrodes of the candle, candles with a high glow value (stay cold while working).
Candles are oiled
The insulator, electrodes and body of the spark plug are coated with greasy, oily soot. The formation of oil soot. The reason is the penetration of oil into the combustion chamber, wear of the cylinder and piston.
Candle overheating
On the insulator there is a glazed and rough sintered coating of dark brown or black-gray color with a crust on the end of the insulator. Wear of electrodes, especially the central one. Surfaces are rough or corroded. The cause may be a lean mixture, damaged spark plugs, valve leaks, or spark plugs with a low glow rating that cause them to overheat.
When using leaded fuel, the insulator is normally grey. Clean the gap between the insulator of the central electrode and the body with a strong sand jet. When screwing in the spark plug, check the cleanliness of the threads on the spark plug in the cylinder head.