Well usually I measure vacuum with a gage on the intake, at idle you shouldn't feel much vacuum at top of carb.
That said, the symptoms sound like dirt in the fuel lines/tank, BTDT - known good carb, put that on, runs good, then craps up like the old one. Usually dirt getting in there. I like those clear plastic FRAM filters in between fuel pump and carb so you can see dirt in an old tired fuel system.
