Sparkplug heat range.

4 replies to this topic
  • Wiz636

Posted December 17, 2007 - 01:18 PM


Has anybody tried a different heat range sparkplug? I know how picky 2T's can be with this but I have never messed around with it on a thumper. Does it make much difference with the hotter temp of a 4T?

  • grayracer513

Posted December 17, 2007 - 02:29 PM


What are you trying to accomplish?

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Posted December 17, 2007 - 02:46 PM


What are you trying to accomplish?

I think he's trying to get more out of his YZ so he can keep up with me :busted:

Actually he needs to slow it down a little but seriously I think the thought of changing a spark plug vs. jetting at the change of seasons or temperatures that we have here in the NW might prove to be a more efficient use of our time... The jury is still out in terms of what a hotter or cooler range of plug will do, something about absorbtion of heat and whether or not that can have enuf effect on the bike running richer or leaner :banghead:

  • Wiz636

Posted December 17, 2007 - 02:57 PM


Don pretty much said it...I'm trying to figure out how to beat him for a change...I'm sick of looking at the finish sheet that says 1st #930, 2nd #636.

In seriousness I'm not really trying to specifically accomplish anything...I'm simply trying to gain knowledge and was wondering if anybody in here has tried using a different plug in their 450 and if it made any real difference in performance, or if it would affect jetting, etc. I'm rather ignorant on the subject of spark plugs and figured that with all the knowledge in here somebody would know something. Even though I'm not necessarily trying to fix anything I wanted to ask.

  • grayracer513

Posted December 17, 2007 - 02:58 PM


It has no effect on the mixture, or the engine's preference for richer/leaner AF ratios, or even how hot or cold the engine runs (with one exception).

The plug heat range is a measure of how quickly the heat at the electrode is carried away, and how hot the porcelain insulator stays while in operation. If it's too cold, the plug will not become hot enough to burn away the oil and fuel deposits that form on it, and it will quickly carbon up or wet foul. If it's too hot, the electrode itself will become damaged. In extreme cases, the plug can become hot enough to become a secondary ignition source, causing pre-ignition, which can cause detonation, and with that, heating and engine damage.

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