You may have accidentally over-filled the unit with oil and the excess oil is being drawn into the cylinder and burned.
It is important to check the oil when the unit is level and some models require checking the oil level with a dipstick screwed full-in or screwed full-out. That, and other model variations for checking or adding oil, can alter the level of oil you would see by a fair bit.
Unfortunately, you did not include a model number for us to confirm the correct procedure for checking or adding oil on your specific model, but your
will cover the techniques in detail.
If the unit is overfilled when checked according to your manual, then you should drain some oil back out to prevent potential engine damage. Even then, you may still see some smoking for a while as remaining oil residue burns away.
Check your air filter also, as excess oil vented into the intake could soak the filter and add to the problem. Again, your ownerâ€™s manual will have details on how much oil should normally be on the filter. If you have a dry paper-style filter and it is now oil soaked then it should be replaced.
If the mower was never overfilled with oil, then the smoking might be due to the protective fuel system coatings applied to new engines at the factory. In that case the smoking should stop after a little use, if not then it might indicate a more serious problem with a head gasket or vent assembly or the piston rings or valves in the engine.