I tuned my blems to 128 as close as I could. My mileage went up a few miles per gallon but the exhaust tips are still getting black after a few days. I pulled a plug and it was full of cabon except on the very tip. Could an exhaust leak be causing a false lean condition causing the computer to compensate? I've checked for leaks but can't find any but you can hear it under heavy throttle at low rpm. What do you guys think, have you ever heard of this?

 

come on nobody knows?