Small Engines (Lawn Mowers, etc.): 22 Toro recycler white smoke then died, crankcase breather, personal pace

Question
We bought a new 22" Toro Personal Pace 60067 in early March of this year.  Have mowed our lawn (1/4 acre) probably 20 times max this year and changed the oil one time since new.  

My son added a little oil before mowing and after about 5 minutes of mowing it started to blow white smoke very heavily.  The muffler/exhaust showed some black oily residue.  We drained the oil from the engine and started over with some fresh oil.  The engine has not run right every since.  Now after mowing for 30 minutes or so it will not start.

What do you think is wrong?  Should I check the spark plug?  Any help would be appreciated.  

Answer
White smoke is almost always too much gas.  My thoughts are too much oil in the crankcase to begin with.  When the crankcase overflowed into the carburetor, through the valves, it has plugged the air filter with oil.  If you haven't replaced the air filter do so.  When you tip the mower, be sure to tip it with the carburetor up.  You could also have a partially clogged crankcase breather due to too much oil in the crankcase.  But I think the air cleaner will be your answer.