Need help for friend who is not going to be around long

Have you tried locking out the secondaries to see how it behaves on the primary side only? A BBC should run very well at 70+ on primary only. If it runs well on the primaries only your problem will be easier to diagnose. As others have said it may need a known good carb because commercially rebuilt Qjet are a crap shoot at best. They are usually done with mismatched parts and very rarely work well.
Good luck and take care of your friend.
Jerry