- 1) light tan is usually considered good; white is typically considered lean but with all the additives in today's fuel, I'd suggest that plug color isn't a very reliable indicator of the proper jetting
- 2) nothing you did, including the filter change should affect jetting. Assuming everything else is stock (no airbox mods, snorkle in place, etc.) then something is up. Check for air leaks on the intake side and exhaust leaks as well.
....did you do anything else you haven't mentioned prior to the backfire/popping issues?
Lastly, stock will work fine, the 22 cent mod is a bandaid that helps but the real cure to KLR jetting is a KLX kit (available from Eaglemike) and removal of the intake snorkle. ....but I'd want to know what is going on before messing with jetting because it shouldn't run like that even with stock jetting.