Not another jetting question... ok it is a jetting question

[Danger]

Here is an example of the correct way to read a plug for jetting purposes. This is the result of a 4th gear plug chop on a new plug. Once the new plug is fitted you need to start the bike and accelerate at full throttle up through the gears for 15-20 seconds then pull the clutch in and hit the kill switch and immeditly pull the plug. A hill is ideal for this and it needs to be somewhere that you do not have to throttle off for a corner or what have you.
The area you need to check is right down inside the plug at the base of the porcelain. This is where a bright light (a pen light will suffice) and a magnifying glass come in handy (if your eyes are good like mine you will be ok).
This is called a smoke ring (also known as the mixture ring).
If the smoke ring at the base of the porcelain is about 2mm and a light chocolate color, congratulations you are jetted very close (or correctly) at this throttle setting (main in this case).
If the smoke ring at the base of the porcelain is less than 2mm, white or very light brown you are lean.
If the smoke ring is more than 2mm at the base of the porcelain or is black, or dark brown you are rich.
You need to use a new plug for each plug chop.
The tan color near the electrode is the result of the burning of the fuel, oil, air and petrol and is not a good indication of jetting, there will always be deposits burnt in this area (unless your plug is so hot that everything gets burnt off this area, perhaps a very lean condition or incorrect heat range plug).
Once you are jetted close on all the circuits then fine tuning can be achieved if needed for your conditions and riding demands over time and by feel.
I typically only use the plug chop as the final test to check the main once the other circuits and the main are dialed in by experimenting and test riding. But it can be useful if you are not that tuned into how a bike should feel by riding or are unsure if what you are feeling is richness or leaness.
Sometimes you just have to put up with a bike that is not jetted at the optimum for the days ride. Jetting is a moving target. For instance I rejetted my KTM only a few weeks ago because it has been quite warm and air screw changes have been adequate. The last few weeks have cooled somewhat so I switched over to my winter settings and because I maybe riding in Taupo soon (different bikes have different change over temperatures, my RM started running lean several months ago and was changed to winter settings then).
Yesterday at the Sandpit it was damp but warmer than the last few weeks. I felt a little rich of idle, but because we were pinning it all day it wasn't a problem and I didn't make an air screw change. If I was putting around I would off. My summer jetting specs would have worked fine yesterday all be it with a rich air screw setting, but I'm not going to pull the carb and change over all the jets depending on the day. The winter jetting would also have been fine with a leaner air screw setting, which would have taken only 10 seconds to adjust back at the carpark but I forgot and only noticed it rich towards the end of the day as the day got warmer and the humidity climbed with the approaching weather. Chances are the next ride will be cooler again and the jetting will be perfect with the correct air screw setting.

[Danger]

A little lean.

[Danger]

A little rich. But notice the nice tan color at the top? Would indicate all was fine if using that method to read the plug.

[Danger]

You might look at a plug like this to check you are in the ball park, but as we have seen in the post above all is not as it seems. The plug does not just remember the last throttle setting it was run at. You could be rich on the pilot and lean on the main or vice versa to get a plug looking like this. Useful for a commercial mechanic trying to get his tractor running right, but not good for a high performance seeking motorcycle racer.
Different fuels and oils will also give different colors. Its the smoke ring that tells the true story when reading a plug.

[Reckless]

Great write up Danger pics and all. That would have taken a bit of your valuable time should help a lot of people though! A lot of guys would not have wanted to part with their knowledge so freely!

"edit" Just had a thought! Not taking away from what Danger has taught you all! But if your not trying to get the max out of your bike in every area or as serious a rider as Danger and the others. The tractor plug is not to far off as long as your bike is pulling well from closed to fully open throttle. I run mine a bit richer than that, I don't foul plugs and the bike still has more power everywhere than I need. Danger prob would think my Ktm 200 was sick, as I have the power valve backed off quite a bit as well. But for my level of ability its better than fighting a race horse every time i ride! Its smooth right through the range and anymore power and I ride like shit! I've only been riding MX 3 years and I'm old so its best to match the bike to the ability.
As a general rule on used plugs the centre electrode color tends to indicate Main or top end and the outer (steel) ring tends to indicate low range. So on a used plug if the outer and inner (as I call them) are both dark and wet you could lower your needle a notch to lean the mid and top. This drops the needle further into the Emulsion tube at full throttle and drops the taper as well delivering less fuel/oil and leaning both areas a bit.

But now we are getting into plug reading used plugs, and that is not what Danger is teaching. He's teaching how to get optimum set up for your bike through out the full throttle range. And he is correct if you set your bike up this way you should only have to look at the plug for safety to make sure its not Grey/white and your lean enough for a seizure. Thanks Danger!

[cheese]

My plug is just black as black.....