What Gord said. Take it out to a field, and put it to work for a half hour or maybe a full hour. Park it, and then start it from cold after it sits for a couple hours or overnight. You may find it has stopped being a juvenile delinquent and has given up smoking completely.
If it had years(hours?) of being fed oil from leaking oil control rings, that will form a coating inside the muffler that will take time to burn off.
Also note that you can get white smoke on ANY engine started from cold if the ambient temperature is cool enough to cause condensation of the vapor in the exhaust gas.
Also note that some are very quick to find inconsequential problems to seize upon as a reason to put down someone else's work. ... And there may be NO solution... as in "that's the way it works, they all do that"
YMMV
tom