Alright, I replaced my spark plugs about 5,000 miles ago, then the other day my car started missing like crazy, so I took them out to find to my dismay that they were covered in a carbon soot. This means I'm running really rich? What are the main causes of this, and how can I fix it. My car is currently throwing no CEL's.
Setup is basically a stock H23 w/ exhaust.

 

if you're running rich you could possibly need a new O2 sensor