1 have you tip it over to clean it
2 is there too much oil in it
3 it may be the oil ring's
if you have tip it over to clean it it will come out of the exaust, is it water cooled that will also give you the white smoke, or water in the fuel
take off the head and have a look see if the gasket ok then have a look at the ring's.
tony, June 2010