Well I havent ridden my bike (99 KX125) yet this year but I'm finally going riding this week. Back in October/November I made some changes to my jetting after getting a PC pipe/can.
The stock jetting is:
Main: 158
Pilot: 45
Clip: 3rd
Airscrew: 1.5 turns out
I experimented with a 50 pilot and the 2nd clip position, but ended up putting it back to stock, but changin the main to 152.
Current setup is:
Main: 152
Pilot: 45
Clip: 3rd
Airscrew: 2 turns out
Needle: stock
The bike seems to run well (with the exception that it sometimes is hard to start) and definately makes more power than stock. However, I'm not sure its running "best".
I know it matters more how it rides than its behavior at idle, but for example. If I fire it up and let it idle, when I crack the throttle all the way, sometimes it bogs. Then when I let go of the throttle, it will let out this big puff of white smoke once the throttle drops all the way back down to idle. If I do it fast enough, it will sometimes stall.
Maybe its irrelavant since its at idle. When riding the bike it feels responsive. I never crack the throttle all the way (cause it'll loop out on me) in the manner I just described when it's idling.
Here are two pics of my plug (br9ev-x which is stock). It appears to be optimal going by Eric Gorr's website. The first couple threads are black and the center is "mocha" brown.