Two possibilities - one - the engine has been tipped on it's side/front, and the muffler is full of oil - in which case it will burn off eventually ( check the oil level if this is the case), or TWO - the bore is worn - new engine required.
This assumes that it's not something silly like putting 2-stroke mix for the chainsaw in the mower.....(in which case don't worry about it - will do no harm at all except possible foul the plug)
phil_saunders(a)bigfoot.com
Phil Saunders, June 2011
