The infamous blue smoke coming from the exhaust is a sign of burning oil. You can also verify this by removing the spark plug. You will see a shiny black or gooey appearance on the electrode side.
Now you may have simply overfilled the engine with oil so that is the first place to start. Remove the dipstick, wipe it off and then re-insert. Pull it out and then check the level. On Asian brand engines, you do not need to screw the dipstick into the case, simply dip it in and put it back out.
If the oil level is fine, then something internal may be causing the problem. You could have a blown head gasket, a bad breather valve, your piston rings are worn or the oil seal for your intake valve is bad.
These are items that would be best diagnosed by a lawn mower engine mechanic as they have the proper tools and information to do these tests. You can find a lawn mower shop near you by visiting our Locations page. Let them know the symptoms of your lawn mower engine problems and give them as much information as you can to assist with the proper diagnosis.