I know that feeling when you pay good money and get a crappy job. If you're capable of doing it yourself then the first thing that comes to mind is "I'll do it myself and get it right" So you want to tear it all apart and "find the problem" I would like to stop you right there and consider doing some checks before tearing it all apart.
A leakdown test will eliminate a bunch of questions. If it's smoky, you're likely burning oil since you post that after setting the floats, it's running great. Black smoke could be a very over rich carb setting but if it's running good then I highly doubt it's fuel. So black smoke in this case is probably oil burning. A leakdown test will tell you if you have a piston ring sealing problem or not. If the rings are passing, you know how far to tear it apart. If they're not leaking, then you know you only have to pull the head and do the valve seals.
One of the biggest mistakes "engine builders" make is honing cylinders with 3 stone hones or the ball type hone to resurface the bores for new rings. These types of hones will not true the bores and make them perfectly round. It's almost impossible to break in a new set of rings if the bore are not true and the rings are perfectly round. It's worth every penny to take the cylinder block to a engine machine shop and have them run a precision hone through the bores to make them round again. Obviously, piston to bore clearance must be adhered to.
The other thing that may have happened here is if it was a rebuild with a new set of rings, the rings may not have seated yet. There are a number of different thoughts on how to break in a set of rings after a rebuild and a Google search on this topic will be enlightening to say the least.
And the best part, if the rings haven't seated yet, you don't need to tear the whole thing apart, just run up the engine properly to seat the rings.
