8 is hotter than 9 (toolmanx3)
If you are talking the NGK Iridium plug, lots of offroaders use them. Its probably because offroaders work harder and therefore run a lot hotter than road bikes and need a harder, hotter than normal plug
heat range. 7 is a "hotter" plug. That means it transfers more heat to the cylinder head during operation.
use NGK, which is best for Japanese machines. the specs to your plug should be found in your owner's manual. NGK CR9E or CR8E (hotter plug) you could also get CR9EIX (iridium)
NGK BPR6ES Champion RN9YC Champion Rn11YC4 [hotter plug fights carbon buildup
You can use the following plugs for a cross reference for a Champion CJ8 Denso - W20M-U NGK - BM7A or BM6A (BM6A is a hotter plug than the BM7A) Bosch - WS9EC Autolite Part # 255
actually theres no such thing as a hotter plug or a colder plug it is all about removing heat from the cylinder go to ngk spark plugs .com and check out their web site it explains it its pretty cool.
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ngk BPMR4A
Copper: NGK 5858 (XR4); Iridium: NGK 7189 (XR41X).....
A good substitute for the Champion RC87YCL spark plug would be an NGK iridium spark plug, such as the NGK 7397 (ILTR6G8G) or the NGK 4469 (ILTR5A-13G). These plugs are known for their durability and performance, offering a reliable alternative to the Champion plug.
ngk BPMR7A