Before unscrewing the candles, check that there are no foreign objects in the niches of the candles. Washers, bolts or pebbles in the spark plug holes will destroy the valves, valve seats or cylinder head when the engine is first started. By the appearance of the candle, we can conclude about the operation of the candles, the adjustment of the carburetor, the state of the mixture and the condition of the engine (pistons, piston rings, etc.)
Coal deposits
Symptoms: The presence of soot indicates an over-rich air-fuel mixture or a weak spark intensity. Causes misfiring, difficult starting and engine instability.
Recommendations: Check if the air cleaner is clogged, if the fuel level in the float chamber is too high, if the air damper is stuck, and if the contacts are too worn. Try using plugs with a longer insulator, which increases fouling resistance.
Oiling
Symptoms: Lubrication of the candle is caused by wear of the valve stem seals. Oil enters the combustion chamber through worn valve guides or piston rings. Causes misfiring, difficult starting and engine instability.
Recommendations: Carry out mechanical repairs and replace spark plugs.
Overheat
Symptoms: Porous, white insulator, electrode erosion and lack of any deposits. This will shorten the life of the spark plug.
Recommendations: Check if the glow rating of the installed plugs meets the requirements of the Specifications, if the ignition timing is set correctly, if the air-fuel mixture is supplied too lean, if there are vacuum leaks in the intake pipeline and if the valves are stuck. Also check the coolant level and check if the radiator is clogged.
Too early ignition
Symptoms: The electrodes are melted. The insulator is white, but may be dirty due to misfiring or foreign particles entering the combustion chambers. May lead to engine failure.
Recommendations: Check the glow number of the installed candles, the ignition timing, the quality of the mixture (isn't it too poor), whether the cooling system is clogged and the lubrication system is functioning properly.
Electrically conductive gloss
Symptoms: The insulator has a yellowish color and a polished appearance. It speaks of a sudden increase in temperature in the combustion chambers during sharp acceleration. At the same time, ordinary deposits are melted, acquiring the appearance of a varnish coating. Causes misfiring at high speeds.
Recommendations: Change spark plugs (colder, while maintaining driving style).
Closing the electrodes
Symptoms: Waste products of combustion fall into the interelectrode space. Solid deposits accumulate, forming a jumper between the electrodes. Leads to ignition failure in the cylinder.
Recommendations: Remove deposits from the interelectrode space.
The normal state of the candle
Symptoms: Gray-brown color and slight wear of the electrodes. The number of glow plugs corresponds to the type of engine and its general condition.
Recommendations: When replacing spark plugs, use spark plugs of the same type.
Ash formation
Symptoms: Soft brownish deposits on one or both spark plug electrodes. The source of their formation is the additives used in oil and/or fuel. Excessive buildup can insulate the electrodes and cause misfiring and engine instability when accelerating.
Recommendations: If deposits build up quickly, replace the oil seals to prevent oil from entering the combustion chambers. Try changing the brand of fuel.
Wear
Symptoms: Rounding of electrodes with a slight accumulation of deposits at the working end. The color is normal. Causes engine start difficulty in cold, wet weather and increased fuel consumption.
Recommendations: Replace spark plugs with new ones of the same type.
Detonation
Symptoms: Insulators may be chipped or cracked. Insulator damage can also result from inaccurate spark plug gap adjustment. May damage pistons.
Recommendations: be careful when adjusting the gap on a new spark plug. Avoid engine jerks.
Splashing
Symptoms: After misfiring for a long period of time, deposits can loosen while maintaining the operating temperature in the combustion chamber. At high speeds, deposits flake off the piston and adhere to the hot insulator, causing misfiring.
Recommendations: Replace spark plugs or clean and reinstall old ones.
Mechanical damage
Symptoms: May be caused by foreign material entering the combustion chamber or caused by a piston hitting a spark plug that is too long. Lead to cylinder failure and piston damage.
Recommendations: Remove foreign particles from the engine and / or replace the spark plugs with shorter ones.