Why are the candles black?
A spark plug is a device thatignites the fuel / air mixture of the engine. The color changes the ceramic insulator of the candles, as a rule, due to the deterioration of the engine or the change in the composition of the fuel mixture, carbon deposits gradually form on it, which is why the candles are black. For the same reason, the candles are considered the best indicator of engine performance.
When the candles turn black equally
Why do black plugs sparkle? If all the candles have turned black the same, then the cause may be the clogging of the muffler, the later ignition, the enriched fuel mixture. About the clogged muffler speaks increase of concentration of harmful substances in an exhaust gas and the raised back pressure of the fulfilled gases. An early ignition can additionally indicate strong knocking in the engine. If both reasons are excluded, then it's possible in a rich fuel-air mixture.
When one candle turns black uniformly
Why is the black candle on the candles uneven? If only one of the set of candles has turned black, this may indicate a malfunction of the candle itself, a malfunction of its wire or tip, or a malfunction of the cylinder to which it corresponds. To locate the cause, swap the black and any of the white candles and make a 15-minute drive by car. If the black candle has become purer, and the clean one, put to it for replacement, has become black, it means a malfunction in the cylinder. If the candles do not change color, then the reason is in the candle. Ideally, you should not replace the candles with places, but replace the kit with a new one and knowingly function, after which the test drive will give a more accurate result: if the new candles remain clean, then the reason was the malfunction of the candles themselves.
When the candle turns black unevenly
When you have black spark plugs, the reason can behiding in a leaking valve, its burn-out, imbalance of the timing belt, or a violation of the exhaust capacity of the exhaust system. In this case, the candle turns black only on one side. If only the cone of the ceramic insulator blackens, and the tip remains light, like the electrodes, then the candle does not match the engine by the calculating number, and it needs to be replaced by a hotter one. If the cone remains clean and the tip of the insulator turns black, the candle on the contrary is too hot for this type of engine.