For bars, I'm using the Renthal Fat Bar Henry bend, which is identical to the stock bars (the '03's come with the Henry bend). Scott's has a deal where you can get the oversize perches and bars for 100$. Bar's are a personal thing, but the bar/seat realtionship on the KX seems a little "chopper like" to me.
For jetting, I'm running much leaner than stock (not unusual for any 125)
1 notch leaner on needle
1 step leaner on the main or stock.
I could probably run a 30 pilot (couldn't find a 32.5).
I haven't noticed any pinging, but the KX seems kind of finicky regarding the fuel it digests. I use a little race gas to keep things consistent.
Smashed the stock pipe beyond recognition, so I put an FMF fatty on it, hoping to accent the KX's strong mid, but I'm not all that impressed with the pipe. It could help when trying second gear starts on loose soil, but I got a 125 so that I could scream the snot out of it. Plus, it doesn't sound as cool as the stock pipe.
Suspension seems to take a long while to break in, works great on jump landings, big whoops and would work well on small, sharp whoops if the rider would just pin it.
I've had some trouble with high speed "chuck holes" found in off road type courses - the rear seems to bottom, but it may be just the opposite (too stiff). Still working on that one, but I've turned the compression clickers on both ends to much stiffer than stock, and I like it better there.
I may finally get to race it against the big bikes at a vet moto race (Starwest) this weekend, but the competition is tough in the OTHG. :confused: