Small Engines (Lawn Mowers, etc.): help me, question pool, needle valve

Question
what are some of the main causes gas gets into the oil?
how does gas get into the cylinder.

Answer
I just saw this anser in the question pool.  The main reason gas gets into oil is because of a sticking inlet needle in the carb.  It can be caused by a sticky needle valve or dirt that has flowed from the tank to the carb and is keeping it open.  It doesnt take much...an eyelash can cause you grief.  Hope this helps.