[pdwestman]

1. Here's what came out of my carb. It appears to be a KLX needle kit! I hadn't expected this as I thought the bike was bone stock. When I purchased the bike two years ago (with ~1200mi on it) the dealer mentioned that they tuned the carb, but nothing about an aftermarket carb kit.

I also noticed this writing on the carb for the first time, and I can confirm that the main jet I removed was a 142 and the air/fuel mixture screw had been backed out 2.5 turns.

Too the well trained eye that Short Top Stem above the circlip on that mid-range needle suggests it was a DynoJet Kit.
Both the needle & the taller headed main jet are probably stamped "DJ xxx". Use a magnifier.

A Properly installed KLX jet kit would have had 1mm thick brass spacer installed on Top of the circlip to prevent the needle from 'floating' up & down under the white plastic needle retainer. The DJ needle should have had 3 thin shims stacked on top to do the same.
The KLX needle has a taller Stem above the circlip grooves to retain its spacer. (ID# N1TB)

The DJ main jets are Richer size for size than Keihin main jets. The Keihin main jets have a stylized 'K' near the size #.

Your bike was possibly running richer than necessary with that previous jetting set-up, reducing fuel mileage and causing the exhaust to run cooler.

 

[pdwestman]

I'll ride it for awhile and maybe swap back in the DJ kit just to compare.

Dave Pelletier could give you his suggestions on which clip groove, shim or no shim & Keihin Main Jet to use with your old kit needle, if it is indeed a DJ needle. (Did you use a magnifier?)

There is one more jetting kit Out-There, JD Jetting. Not to be confused with DynoJet (DJ). Can't remember if Dave has a pic of a JD needle or any experience with one.