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Canadian Daves JustKDX
Yet another jetting question!
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[QUOTE="Rich Rohrich, post: 1381970, member: 16241"] Plug heat range isn't a tuning tool. It's a matter of getting the plug to run at a temperature that is hot enough to stay clean of deposits that can cause fouling while maintaining a temperature low enough to keep the plug from becoming a source of ignition before the normal firing point ( pre-ignition) . The engine parameters influence the plug heat range required not the other way around. The OEMs choose a plug heat range based on how long, in seconds, the engine will be expected to operate at full load, full throttle. They are thinking worst case with these tests. A "cold" spark plug is one with an insulator nose shape that conducts heat more readily. Because it can transfer heat from the nose to the large mass of aluminum in the head quicker it can resist full load heat build-up longer. Eventually given enough time at full load it will eventually reach a heat saturation point where it will act like a glow plug and fire the mixture without a spark. Motorcycle OEMs tend to err on the cold side with their recommendations for two-stroke plugs as a safety measure, but a spark plug that is too cold will foul easily and not be able to reach high enough temperature to clean off the deposits that cause short-circuiting of the spark and eventually complete fouling. Hotter plugs work well when the loads tend to be low or the engine spends a lot of time at part throttle and this is followed by relatively short bursts of WOT throttle. What this all adds up to for out purposes is the heat build-up and subsequent running temperature of a spark plug is largely determined by engine load, spark timing, jetting, and cylinder head heat dissipation. The important thing to take away from all this is, hotter plugs to NOT raise the engine temperature on their own, and they do NOT add heat to the engine. That's the thing that seems to be the point of greatest misunderstanding in all this. [/QUOTE]
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Dirt Bike Discussions By Brand
Canadian Daves JustKDX
Yet another jetting question!
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