The B&S Inteks and some other slightly different models are known for the head gasket failing between the two bolts that are on the piston/cylinder side of the pushrod channel(?). The two bolts are out at the periphery, and the gasket goes from top to bottom, so has a good span w/o a bolt. There is another(more?) head bolt further away, past the pushrod channel, so the head is not going to fall off, but they do fail. When that happens, two things are possible, one being soot & oil being blown down onto the chassis, or over-pressure in the crankcase, leading to oil getting pushed out the breather, and pressure-fed to the valve guides, thence the combustion chamber.
Same thing can happen on a Kohler, but I don't think it is as common. If the head gasket allows gas into the crankcase, it will raise the pressure, and push oil & mist.
I don't make a practice of removing the dipstick tube cap when an engine is running, as it WILL blow stuff out at you, no matter the condition of the rings. There is a piston(or more, depending) going up and down, changing the internal volume back and forth as it strokes. There should be a flapper valve or a diffuser or myriad(maze) separator behind the port for crankcase ventilation on the rocker arm cover. With normal flow, it is able to catch the liquid droplets, cause them to fall out of the airflow, and drip back into the crankcase. If overpowered with flow, oil will get into the intake, burn, and cause blue smoke. I have not taken apart either CV I have to inspect for exactly what is in there to limit crankcase flow, but most OHV rocker covers have a maze to slow down or catch the oil.
You can remove the cylinder head and check the gasket, you can inspect the breather element stuff, and also inspect the other parts that seal the crankcase.
You can make up a 'manometer' to see if a slight vacuum is developed in the crankcase or if it will blow the water out of the U-tube(rubber/clear tubing filled with water, U-shaped, one end open to atmosphere, other end connected to the breather tube port. Your own fake amateur manometer w/o gauge...) Check youtube for vid examples.
tom
