My YFZ runs like crap when ever I'm not giving it gas. As long as I am giving it gas it run great. As soon as I back off the throttle and run at a steady speed, it acts like it's running out of gas. It won't idle, and sputters real bad at full throttle, top speed. I pulled the plug and it was black, telling me it's running rich. It doesn't pop on decel. I have a LRD Pro Series 4 Pipe, no lid, KN filter. No other mods that I know of. I bought the bike used from a local dealer. 172 main, 45 pilot, don't know what the needle is set at. I have tried the fuel screw at 1 turn out and 3 turns out, not making any difference at all. I ride at about 1500 feet, between 70 - 85 degrees. Any suggestions?