Correct me if I am wrong, but smoke from the breather or PCV is probably blow by. This is exhaust/partially burnt fuel fumes coming past the rings during compression, into the crank chamber and exiting out the heads via the breather/pcv. Theoretically, this should enter the intake via the pcv and get reburned, but if you have excess is blows around the seal. Since you have a fresh rebuild, you could have a ring that is not seating properly which could be creating your issue???. I know when my rings wore out, I started having smoke out the breather...blow by is a pain. Do a compression test or have someone do one to check for ring seal issues.

 

there's a grey area to this. some motors naturally have "blow by". my motor from rebuild, and a few others I know have crankcase pressure with full compression in all cylinders. if this is the nature, you just need a good valve cover baffle to prevent oil from entering through the pcv, and let the carb draw the steam.