Stuck to the top of this forum, the 'Every kdx rider should read...' thread links CDave's site. He has listed stock jetting for kdxs there. Also baseline jetting changes for different basic modifications.
You mention 'carb tuning' which is on CDave's site, so maybe you've been there. It tells you most everything you need to know.
Cdave's 'Just kdx' and this board, although hosted by the same folks, isn't the same place.
Chance of running too lean is certainly possible. Highly unlikely, though if you observe common sense in jetting.
Common sense is: Knowing what your starting point is, what you want to change. Observe plug condition and engine response to arrive at correct jetting for your situation.
Common sense is not: Putting a jet sequence in your bike based on what **someone tells you** on this board with no regard to why or check of the outcome in your situation.
You CAN have a plug that is black from a bike that is lean enough to stick under WOT operation...if the jetting is off far enough in just the right places.
It's not rocket science...but being informed, advised (not told) and doing your own jetting is the only way to go.
The recommendations on CDave's site are straightforward, correct and not anything that will get you into 'too lean' trouble (other mech problems notwithstanding).
As an example: A dealer (or anyone else) that tells you to change from 32:1 to 40:1 to 'lean out' your bike, and in an attempt to stop fouling plugs is at the very least completely, absolutely wrong.
For one thing, you are making the air/fuel mixture richer not leaner. Secondly, a plug fouling issue is much more likely air/fuel related than anything else.
There isn't anything wrong with 40:1 in the kdx in the large majority of cases. But it's air/fuel that's the problem...and that is resolved with proper jetting.
In many fewer words: 'It sounds like your bike is running rich.' ;)
(refer to asterisks inserted above!)