I've had multiple problems with rebuilding my MKIII. New Emgo .020 pistons, new valves, guides, springs, E-ignition,coils, blah blah. The bike would miss under acceleration and kept getting worse. Pulled the plugs and one was very oil fouled. Pulled it apart and this is what I found. Left side has a scored cylinder, right side is good but burning oil. Did a leakdown on both cylinders, both are leaking out the exhaust valves. maybe 150 miles and I'm prety tired of this crap. Brought the head to the machine shop that did the work. they will disassemble and call me. this is a performance shop that has worked on Nortons and Triumphs and is well regarded.