What could cause oil to leak into the carburetor on a ';Wright Stander'; Mower.?

I work for a landscaping company and today when i started the engine to the mower I saw a huge puff of smoke come out and then it continued to smoke after running for a minute. I then shut the mower down, removed the air filter, and took a peek inside the carburetor. What I saw was a small puddle of oil inside the carburetor, The type of mower is a WRIGHT STANDER and it has a 19 hp YAMAHA engine. Unfortunately our mechanic is out of work for the month due to a ';shredded'; nerve and can't make it in. Any feedback will be greatly appreciated.What could cause oil to leak into the carburetor on a ';Wright Stander'; Mower.?
was the mower tipped just before this? like to change the blades or a belt? this is the most common cause. second would be a badly clogged air filter. either way, what is happening is oil is coming through the crankcase breather into the air filter housing. if it has a paper filter, make sure it's not oil soaked- replace if so.What could cause oil to leak into the carburetor on a ';Wright Stander'; Mower.?
the odds are that the oil was from the breather for the crankcase. this is a hose that alows fresh air (filtered) to enter the engine block. I would guess the engine may have a pcv valve that may be plugged or sticking. this is usually the cause of the oil in carb condition. normally blowby vapors are drawn into the intake by the pcv valve line