Spark Plug reading

True dat.

Back in "the day" when our fuel had lead in it, plugs ran tan. Now, we are looking for more of an off-white.

Which is why I cringe hard when someone posts that awful plug chart from the Haynes manuals. It was probably made from plugs pulled from a Model T. I've never in my life seen a plug that really matches anything on there; of course I'm a young'n and have only ever had unleaded fuel to play with.

What the world needs is a cheap 4-gas analyzer and a good DIY drum dyno...

Yeah, that plug chart you are referring to qualifies as "misinformation." Whole 'nother matter with modern fuels.

I am on a lot of Harley forums. Sometimes a guy will post complaining of poor gas mileage, like 35 mpg. A properly tuned Harley will get 40-47 mpg. They will say things like, "My plug is a nice tan color, so I know it's not too rich." Of course, on a Harley, that IS too rich. A proper reading on a modern Harley plug is almost white with no deposits.

Yea, HD use a really 'soft' plug stock, equivalent to a NGK BP5~6 if I recall correctly? (I forget all the suffix for HD, it's why they have application charts ;D )
BTW, my 378 is getting close to stock 883 HP 8) (not torque though )

If that was taken out at WOT plug chop, it's close enough, but a shade rich - better cooling though. We need to see inside the plug for jetting. The side steel part is not a good indicator of jetting IMHO.

Plugs can only be read at WOT under load. AT low load, they are not hot enough to burn clean.

http://www.strappe.com/plugs.html
That's an old reference but still the best.

i agree with teaser on this....you can not accurately read a used plug for JETTING purposes it is only good for a quick snap shot of average running.....and you need to read where the ceramic and metal meet deep in the plug after a new plug is installed and a plug chop done. i do not think you will see it in a photo unless you have one hell of a camera/lighting set up....joe@ v cycle