The problem is due to a poor design and the crankcase can't vent correctly. None of my current collection of bikes blow oil out. When I first started increasing the RPMs the pressure built up and could empty the crankcase in about 15 miles at full throttle.
The vintage motors had a cavity at the upper rear of the crankcase and a breather to reduce the pressure. When the new edition motor was designed........some idiot in Taiwan didn't understand the theory of liquid pressure. He thought reducing the size of the cavity would help the case vent, but in fact it made the pressure very high.
When the NE cylinder was developed a hole was placed at the base of the tappet cavity and now allows the crankshaft to sling the oil directly into the chamber. It doesn’t take long to fill the area and start pumping the oil out the vent hose. Once the oil starts to vent it creates a siphon effect and can purge the entire crankcase in a short period of time.
I have developed many fixes over the last several years, and the Taiwan vendor reproduced some, but he always had to put his "spin" on the concept and always managed to goof it up.
The object is to separate the air from the oil, and have the oil return to the crankcase.
Here are all the fixes.........First the hole in the base gasket must be reduced. I use a WC-1 gasket and cut a slot to open only half of the hole, reducing the amount of oil sprayed into the tappet cavity. I also make a special aluminum tube to make the oil hit the top of the lifter cavity [approx. 1/8" from the top]. I then drill 2 small holes at the base of the tube to allow the oil to drain back into the crankcase. The last and most effective fix is to make an external breather. The external vent should be 6" long and 1" O.D. You can use PVC tubing and glue to make the cylinder. Install a nipple at the bottom of the tube and attach the hose from the compression release cover [used on the NE motors]. If you have the WC-1 cover, drill and tap it to install a fitting to attach the hose. Next fill the tube with COURSE pot scrubber material [don't use steel wool as the vendor in Taiwan did]. Next install a PCV valve in the top of the tube to cause it to pulse. The pulsing causes the air and oil to separate and allow the air to escape.
It is also important to note the vintage motors had cam ground pistons and were NOT round. The round piston on the new edition motors causes "blow-by", but can be controlled by the breather system.
I guess I will need to start making breathers to help solve the problem.
Have fun,