Whoa! Your Mower is Smoking:
This might look a little scary, but it's usually not serious. Your lawn mower's engine can smoke if your oil chamber is too full (overfilled), or if oil has leaked into the exhaust muffler when you tilted your mower to the side. It's simply burning off while the engine is hot and it will soon clear. Wipe up any oil that may be underneath the exhaust.
If the engine stops or won't start, check and clean the spark plug and air filter. If you are unlucky, perhaps oil has got into the carburetta and will have to be cleaned out by a service agent ( repair would not be covered under warranty) .
Always ensure that the correct amount of oil is showing on the dip stick ( refer to owner's handbook )