Run less oil in the sump, there are several post in the 4 Stroke section that say that the 511 is quick to blow excess oil out the breather and into the airbox, the only solutiion being to run less oil in the sump.
When refilling your oil level, make sure it barely touches the bottom of the sight glass. Run your engine for ten minutes to heat the oil, recheck oil level to make sure that it is at the very bottom of the sight glass.
