I'm not in the landscaping business but I have lots of grass to cut each week! I have a 2004 B/S 16.5 model #310707 that smokes when the blades are engaged or when it is run at full throttle. The engine will also foul the plug with oil in 20-30 minutes. I do no see any oil in the carburetor or the breather tube. The oil also becomes dark quickly. I have done some preliminary test and inspections: tune-up The compression is 90-100 psi I did not do was a leak down test. removed and inspected breather disassembled and inspected carburetor installed new carburetor removed cylinder head and disassembled. I found oil in the intake pocket of the cylinder. I also found oil deposits on the back of the exhaust valves. the cylinder bore still has a nice cross hatch. when I coat the bore with oil and turn the engine by hand the rings seem to clean the cylinder OK. At this point I'm planning on cleaning and lapping the valves,replacing the head gasket,changing the oil,replacing the breather,replacing the dipstick tube o-rings. If any one has seen this before or has any ideas that could help I would appreciate it. Thanks!!