Pete, i dont think you have an oil problem. The fact that the mower was left standing with the plug facing down is the reason for your oil problem. Grab a new plug or hot run that one in another mower to burn off the excess oil. Get some degreaser/carby cleaner and spray through the carby to clean your inlet and through the plug hole to clean the piston/bore. Pull the starter 10-20 times with no spark plug fitted and throttle control in the off position, so you dont get a fire, in order to discharge the excess. Refit plug and start the mower.
