You say it's running rich, and you said the rpms climb with the booster vacuum line open.
It's to rich. the engine wont run well if its blackening the plugs. Find somone that knows how to tune these carbs ON THE CAR.
Everything you've stated tells that the engine wants more air.
Get the Air/Fuel ratio where it needs to be, change the engine oil, and maybe the leak down numbers will also improve. You are chasing a tuning problem, not a mechanical issue.