After about a 600 miles of driving the area around my exhaust tips get discolored with carbon build up. The only way it comes off is with a fine cut buffing compound. Is this caused from me not having a catalytic converter or is it running rich? I don't smell any unburned gas at idle or after a drive.

Carbon Build Up
After Light Buffing

 

Probably from not having any cats. Mine doesn't build up like that but the inside of my tips has some build up in them. I not running any cats either. I guess the reason mine doesn't get on the body is my tips stick oout about 1" past the bumper.

 

I dont have that problem but i still have the stock cat. The carbon should come off with a clay bar.

 

I make soot even with cats