I have a 95 Civic Cp 1.6 L with a K&N, stock hedder, stock cat, stock exhaust, and a Hayame universal muffler.

I'm getting like 20mpg and I'm noticing black exhaust comming out. Not extreamly noticeable but deffinetly in the high RPM's it shoots out a bit of blackness. Anyone know what this could be do to? Anyone know what I can do to fix it? I'm gonna get some fuel injector cleaner and see if that does the trick along with swapping out the plugs with some colder ones like Bouche + 4's....

BTW ~ I've noticed a black stain above my muffler on the rear bumper. It's been there for about a month and a half.

Also, my car got jacked. Did the theifts rev the shiat out of it and fawk up some internals? Is it possible?