Compression is fine. Theres no vacuum on the fuel pump at all either. It doesn't even dribble. I'm guessing they're sucking in as much air as the carb is, reducing the amount of suction on the carb. There is a little there, but not a lot.
Good news, at least the carb actually says mikuni on the side. And it definitely looks original. He said he replaced the carb... sounds like another one of those "tall tales" sellers tell