Confused on heat range and plug gap

[GeoffM24]

When I bought my bike used it had a NBK BR9 type plug with the gap adjusted to a "8" range.

When ?I went to NGKs website they say the 9 or 8 stands for the size of the gap but I was under the impression that was heat range.

So is the 8 and 9 for heat range or gap size?

Thanks

 

[EricGorr]

The spark plug gap on a modern 2-stroke dirt bike is .020-.024 inch.
With NGK plugs, the number is the heat range, the higher the number the colder the heat range, meaning that the plug transfers out heat more efficently.

 

[GeoffM24]

Thanks Eric.

The plug that was in the bike was not fouled but very black and oily, a sign of running rich I take it.

I have your book and read it over and over and I read that part about what you said in regards to jetting specs and magazine specs. I got the impression that you thought they were of little value.

I invested in a old issue of Dirt rider where they tested my 99 Rm 250 and I read where they chenged the jetting to a 152 main, changed the needle position from 3 to 2, set the air screw to 1 1/2 turns out so I did the same on my bike except I went with a 152.5 main. I also checked FMFs recommened changes as well as Bill's pipes and they all seem to agree on those changes. I also added a Rad valve which also suggests leaning the bike out.

I switched the spark plaug back to the correct heat range. I have a FMF Gnarley pipe and shorty silencer along with the rad valve. I run 32 to 1 and my elevation is about 100 feet above sea level. I set the jetting for the warmer weather of spring/summer.

I am hoping this will give me a well jetted bike if not a good baseline.

Any thoughts?