A spattering of BS input from this end (maybe the top-end..maybe not)...
re: 'To tell you the truth Al... I have never heard of a KDX fouling a plug.'
That's quite the sheltered life!
Shirley, you must be joking!
Happens all the time. Generally due to an improperly jetted machine.
Generally speaking, one side of the crank will suck air (LH), the other will suck oil (RH). If you're sucking enough oil to make a noticeable smoke difference, you will see a change in trans oil levels. Well..that is if you
check it at all..and you did. Like LT said...the smell would be a tell-tale, too.
After a point the number of miles/hours on any machine isn't as important as the number of
years it's been around. An '04 with 600 miles on it is not the same thing as a '91 with the same 600 miles. Time is
not your friend in that regard. Seals get hard, fuel and oil turns to goo etc. etc.
120psi is pretty low. May be another age issue. Rings may well be stuck.
'Sump' I suppose is a reference to the crankcase area..under the piston. It's not a sump, but understood just the same. Yes..fuel/oil (premix) can pool there for a variety of reasons. You shouldn't have TRANS oil in there. Any such pooling isn't something that will be a problem for an extended period of time. Airflow thru the area and agitation of the spinning parts will disperse it fairly quickly.
When you get the cylinder off, let us know what condition the rings are in. They should be springy and freely moving NOT stuck in the piston lands as if they were glued.
Here's a btw..If you get a set of rings with the wavy little ring insert that is supposed to fit UNDER the ring? ...leave it
out on re-assy.
As long as the cylinder is off, might as well take the carb down to metal parts..soak it in some Berryman's.
And...what's all this malignment of my good name (thass'a joke, son!)? Besides, it seems all the references to Mr. W. are moot what with the current picture of him (?) in a SKIRT for crine out loud! And the location is still 'in the shower?' Face it. Mr. W. is not well. He has traded time riding for time spent taking pictures of his nekkid self and posting them for the world to see. That's so sad......

Yeah, I
could have taken the pic..but I would've needed a blindfold and a telephoto lens the size of a semi truck! Well, that a whole lot of $$ I suppose....