Small Engines (Lawn Mowers, etc.): smoking lawn mower, combustion chamber, white smoke

Question
I am going to buy a lawn mower that smokes a very white smoke but it's only once every 30 or 40 times it's used and only lasts around 45 seconds or 1 minute. Should I be concerned or is it just a problem caused by old gas or oil?

Answer
I can only make a guess based on the symptoms so please take it as such.

Either the mower is being stored every once in a while so that gas is leaking into the combustion chamber or engine block or the needle isn't seating in the carb sometimes.  

Either one of those is simple to correct.  

If you have any more info about this or another question, just let me know.  Thanks, PK.