Stihl: BG56, BG66, BG86, SH56, SH86, BR200, BR500, BR550, BR600, BR700, BT131, FC56, FC70, FC90, FC95, FC100, FC110, FS25, FS40 (Ø10mm Plug engine only), FS50, FS56, FS65, FS70, FS56 (Ø10mm Plug engine only), FS87, FS89, FS90, FS91, FS94, FS100, FS110, FS111, FR130, FS130, FS131, FS240, FS260, FS310, FS311, FS360, FS410, FS460, FS460 C-EM, FR410, FR460, FR480, MS150, MS150 C-E, MS170, MS171, MS180, MS181, MS181 C, MS192 C-E, MS193C, MS193T, MS201, MS211, MS211 C, MS231, MS241, MS251, MS241 C-M, MS362, HT100, 101, 130, 131, KM56, KM90, KM94, KM100, KM111, KM110, KM130, KM131, HL90, HL91, HL94, HL95, HL100, HS81, HS86, HS46, HS46 C-E, HS46, HS56, HS56 C-E, HS81, HS82, HS86, HS87, HT56, HT100, HT101, HT102, HT103, HT130, HT131, HT132, HT133, MS 201 T, MS 201 TC, SH56, SH200, SR200 This spark plug has a resistor that is produced with a glass and carbon mixture, which is fired to ensure superior performance and durability. It has corrugated ribs that prevent flashover and cold rolled threads to inhibit damage to the cylinder head. Some types of fuel additives in lower quality fuels can cause spark plug deposits that can lead to misfires, pre-ignition, etc. NGK is the brand leader in the UK spark plug market and are the world's biggest supplier to many major car manufacturers. Each and every one of their products are designed to meet the most rigorous standards and are the professionals' choice because of their quality and technical excellence. Their plugs can be found in use by teams in F1, WRC and MotoGP. Put simply, NGK genuine spark plugs are the workhorse at the heart of smooth-running engines around the world.

The spark plug heat range has no relationship to the electrical energy transferred through the spark plug. The heat range of a spark plug is the range in which the plug works well thermally. The heat rating of each NGK spark plug is indicated by a number; lower numbers indicate a hotter type, higher numbers indicate a colder type. Air (atmospheric) pressure and cylinder pressure decrease as altitude increases. As a result, spark plug tip temperature will also decrease. The union nut (1) of a STIHL spark plug is fixed in place. This ensures there is no spark gap which could impair performance or potentially ignite gasoline fumes. Husqvarna: 345FR, 439, 526XP, 545, 545FX, 545FXT, 545RX, 545RXT, 550XP, 550XPG, 555, 556, 560XP, 560XPG, 562XP, 562XPG, T435, T540XP, T540XP 11 The spark plug firing end temperature must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called “thermal performance,” and is determined by the heat range selected.

Types of Abnormal Combustion

A hotter heat range spark plug has an insulator design with a longer heat flow path to the metal shell of the plug. As a result, more heat stays in the ceramic firing end and less is dissipated to the engine. A colder heat range spark plug has an insulator design with a shorter heat flow path to the metal shell of the plug. As a result, less heat stays in the ceramic firing end and more is dissipated to the engine. For a spark plug to function properly, it must have a tip temperature high enough to burn off carbon deposits (self-cleaning) and avoid fouling, while remaining low enough to avoid overheating the ceramic firing end and pre-ignition.

A colder heat range spark plug may be necessary due to the increased cylinder temperature as boost pressure (manifold pressure) and subsequent cylinder pressure and temperature increase.

Spark plugs must provide a path and a location for electrical energy from the ignition coil to create a spark used to ignite the air-fuel mixture. A sufficient amount of voltage must be supplied by the ignition system to spark across the spark plug gap. This is called “electrical performance.” This spark plug has a resistor that is produced with a glass and carbon mixture, which is fired to ensure superior performance and durability. It has corrugated ribs that prevent flashover and cold rolled threads to inhibit damage to the cylinder head. Features & Benefits: The heat range must be carefully selected for proper spark plug thermal performance. If the heat range is not optimal, then serious trouble can be the result. The optimal firing end temperature is approximately 500°C (932°F) to 800°C (1472°F). The two most common causes of spark plug problems are carbon fouling (< 450°C) and overheating (> 800°C).

Mismatched ignition system components (plug resistance/wire resistance, ignition coils/igniter modules, etc.)

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https://www.ngkntk.com/newsroom/feature/emea/2020-1/counterfeit-spark-plugs-the-ignition-villains-that-could-ruin-your-engine/ Pre-ignition occurs when the air-fuel mixture is ignited by a hot object/area in the combustion chamber before the timed spark event occurs. The NGK Standard Spark Plug is constructed from durable material that is corrosion and abrasion resistant. The spark plug insulators are made of 99 percent pure alumina silicate, allowing for longer insulator noses for reduced fouling. This spark plug features a triple gasket sealing process that eliminates fuel leakage. It also includes a solid copper core that provides superior heat dissipation and conductivity. This spark plug has resistor that is produced with a glass and carbon mixture, which is fired to ensure superior performance and durability. It has corrugated ribs that prevent flashover and cold rolled threads to inhibit damage to the cylinder head. When the spark plug firing end (tip) temperature exceeds 800°C, pre-ignition originating from the overheated insulator ceramic can occur.

If the engine is to be operated at high RPM, under a heavy load or at high temperatures for long periods, a colder heat range may be needed. This spark plug features a triple gasket sealing process that eliminates fuel leakage. It also comprises a solid copper core that gives superior heat dissipation and conductivity. Spark plugs have been around as long as internal combustion engines have and are often a misunderstood component. This basic guide is designed to assist the technician, hobbyist or race technician in understanding, using and troubleshooting spark plugs.Carbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450°C (842°F). Carbon deposits will begin to burn off from the insulator nose when the self-cleaning temperature is reached. When the heat range is too cold for the engine speed, the firing end temperature will stay below 450°C and carbon deposits will accumulate on the insulator nose. This is called carbon fouling. When enough carbon accumulates, the spark will travel the path of least resistance over the insulator nose to the metal shell instead of jumping across the gap. This usually results in a misfire and further fouling. There are many external influences that can affect the operating temperature of a spark plug. The following is a brief list to consider in avoiding reduced performance and/or expensive engine damage. Engine Speed and Load Image are for illustration purposes only and may not reflect dealer inventory or unit specifications. Excessively rich air-fuel mixtures can cause the plug tip temperatures to decrease and carbon deposits to accumulate, possibly causing fouling and misfires.