Hello all, I am new to forums so please let me know if this topic already exists. Here is my issue. I am a trained motorcycle technician but his has me stumped. I have an 08 xt250 (carbureted) and put the fmf slip-on on it and tuned the carb and it runs fine with no issues. My friend bought a 2014 xt250 (FI) and he wanted the same exhaust. I installed a power commander on it due to the exhaust creating more airflow, needed extra fuel to compensate blah blah blah. What I am stumped on is that his bike starts and runs fine for the most part. But, his bike is throwing me obstacles I’ve never seen before. Normally, I am able to tell if a bike is running rich or lean and they usually only show symptoms of one or the other. Here are his symptoms (I will add whether I believe each respective symptom is a reach or lean symptom beside) -exhaust melted rear fender (lean) -sooty residue on fender (rich) -when cold, slight hesitation under acceleration (lean) -backfiring under decel (lean) -the spark plug electrode looks clean, but the threads are black (stoich/rich) So the bike in my opinion is showing symptoms of being rich and lean. The power commander that was available for this bike was a non programmable unit, but is does have manual dials to adjust as needed. I am under the impression that it is lean, but the black soot on the fender is the major issue that is throwing a wrench in my gears. The map that is installed on this PC is an “optimized stock” map, so it obviously could still be lean, which I understand but the black soot is throwing me off. Anyone out there had the same issue with this bike/muffler combination? I plan to add more fuel with the manual adjustments on the PC (since I feel there’s more lean symptoms than rich). I would appreciate any input. Sorry for the long post in advance.