Motorcycle Questions? Ask a Mechanic.
Are you confident he fully rebuilt it? The reason I ask is that kind of smoke is caused by one problem and that is a cylinder issue. It can be as simple as the need for new rings or as complicated as the need to bore the cylinder to return it to round and/or remove taper.
A "fully rebuilt" engine would include measuring the cylinder to verify it is round and not tapered, honing/deglazing if it measures good, and intalling new rings.
If the problem is the same as before I'd guess that the cylinder work was not done or not done properly.
I hope this helps. Thanks, P.J.