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Honda UK CX500-C-B and US 1979 to 1981 CX500 C, 1979 CX500 D

Source: Haynes, Honda CX/GL500 & 650 V-Twins Owners Workshop Manual
See my other post about Honda CX500
and also my post about DIY cx500 CDI
car review, motorcyle review, automotive tips, 4wd review and tips, pre-owned car review, automotive review
Note: This is the last posting for Spark Plugs, see my previous posting for spark plugs.
Pre-ignition
Detonation
Misfires
Fouling
Below is a list of external influences on a spark plug's operating temperature. The following symptoms or conditions may have an effect on the actual temperature of the spark plug. The spark plug cannot create these conditions, but it must be able to cope with the levels of heat, if not, the performance will suffer and engine damage can occur.
Air/Fuel Mixtures seriously affect engine performance and spark plug operating temperatures.
Advancing Ignition Timing
Engine Speed and Load
Ambient Air Temperature
Humidity
Barometric Pressure/Altitude
The spark plug has three primary functions:
It is important to note that spark plugs never create heat, only remove it. The temperature at the end of the armature has to be kept low enough to prevent pre-ignition, but at the same time high enough to keep from fouling. The plug also works as a heat exchanger by transporting thermal energy from the combustion chamber to the cooling system. The term heat range is the plug’s ability to dissipate heat from the tip, but has nothing to do with the actual voltage transfer.
The plug’s efficiency is also determined by variety of factors such as insulator tip length, the absorption and transfer of combustion heat, the gas volume surrounding the insulator tip, and the construction/materials used in the center electrode and insulator. Regardless of spark plug preference, the difference in the heat range is the measured ability to remove 70 to 100 degrees from the combustion chamber. The longer the spark plug tip, the longer the travel of heat before it is absorbed by the cylinder head, retaining more heat equaling a hotter plug. Conversely, a shorter tip equals a colder one.
Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. Conversely, if the tip temperature exceeds 850 degrees, the ceramic material around its tip will blister, causing the electrode to melt. The temperature range between 450 and 850 degrees is loosely defined as the spark plug cleaning region. At these temperatures, the accumulated deposits burn away from the center isolator. In addition, this region has no bearing on spark quality or its intensity.
Spark Plugs Selection and Installation