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Discussion Starter #1
Changed the plugs in my 910R this weekend, they were a bit past their best having done at least 35000km ....

The ones I removed were CR8, the book says CR9 and I installed CR9 iridium. The bike is running great again now, what difference would the 8 make compared to the 9 ?
 

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King of Bling
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The heat range of a spark plug is the range in which the plug works well within a specific temperature.

The heat rating of each spark plug is indicated by a number; lower numbers indicate a hotter type, higher numbers indicate a colder type.

A spark plug with a heat range number 8 will give you better cold starting and less likely to foul than a spark plug with the heat range number 9..

However, with hotter plugs there is the danger of burning a hole in the piston under extreme conditions.


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Discussion Starter #4
Thanks John, the colour of the old plugs suggests it was running a bit lean and hot so moving to the 9 (as per the workshop manual) is probably a good idea.
 

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King of Bling
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Hi Richard

The thickness of the plug insulation determines whether it's a Hot or Cold plug.. The Hot plug has less or thinner insulation.

<O:p</O:pIf you’re going to drive the engine hard, then the recommended 9 heat range plug is advised and a safer option as you said. .. If you’re just going to cruise around and not go banzai on the bike, then the 8 heat range plug will be fine and will give you a much better complete fuel/mix burn.

<O:p</O:pSometime engines don’t run to well on cold plugs and tend to struggle with cold starting, foul the plugs in traffic and in serve cases, tend to stall more frequently.

Here's a good link from NGK : http://www.youtube.com/watch?v=LbR75wq9nmM




<O:p</O:p.
 
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