Bought a 2007 Sportster 1200 Classic, 13k miles, bike ran good but developed a miss at a steady speed, around mid throttle range. Bike not riden much over the past year. Changed plugs, plug wires, air filter. Air filter had light black grease on the inside and air intake was a little greasy. Seemed to get a little worse after the work. Plenty of power, seems to idle to low.. Long time rider, but new to Harley Bikes, ideas???