Br'er Rabbit - 2007 DRZ400s

[V1GiLaNtE]

That plug is fine.  Assuming stock pipe and air filter and it runs well, you probably dont need to do anything here.

The fuel mixture screw you're looking at will only change the fuel mix at idle - your pilot, main, slide profile, needle profile are the black magic of making it all work the rest of the time.

Nothing stock about it:

FMF Powerbomb Header
FMF Pipe
3x3 Box mod
Jetting kit
Hi-flow air filter (just installed)

I need to look into it more because the bike is starting to have a hanging idle. Additionally, it's got A LOT of popping on decel where it will occasionally stall coasting into a stoplight with the clutch in. Sorta of like it ran out of gas. The RPMs will dip really low, again like it's running out of gas. Otherwise the bike rips through the gears. I've tried adjusting the idle speed, but have not noticed it making much of a difference. TBD on whether the adjuster isn't working or what. 

I need to check to make sure there isn't a vacuum leak somewhere. Most common issue points to fuel mixture, but want to rule out the low hanging fruit first.