Lawn mower spews white smoke and sputters out?

You could have overfilled the crankcase with oil or tipped the mower and got oil into the air filter. Check the air filter if it has oil on it replace it. If the crankcase is over the full mark drain some out. If you tip the mower to clean Always tip it with the air filter up. Oil will run through the crankcase vent hose into the air filter area, from there it will get into the engine and be burned.