Why did my air filter fill up with engine oil?

Make sure the PCV is actually "sucking". The hose could be collapsed, or more likely the port on the carb plugged up. To clean the port, remove the carb, and using a drill bit by hand, go up through the bottom hole, then go through the nipple for the hose. Also, if you have had the carb off, it might have been reinstalled with the small hole in the gasket in the wrong position.