1. Exactly which vacuum port are you using? Left/Center/Right
2. Is this a new carb on the motor?
2a. If it's a new carb, what carb did it replace?
3. Have you removed the top of the carb to see if the gasket is soaked with fuel?
3a. If the gasket is soaked, is there dirt in the needle/seat?
3b. Is the float set properly?
4. If you take off the distributor cap, is there moisture inside?
5. Have you put a hand vacuum pump on the distributor to make sure the gasket is working and not torn?
Here's what I'm thinking... And this is a shot in the dark.
If I had to guess, you pressure washed the motor, got water in the vicinity of the distributor. The distributor vacuum advance is torn and sucked in the water laying on the bracket. Once inside the canister, it fell to the floor, away from the vacuum stream.
It's black because it's been laying against the black rubber diaphragm in the vacuum advance canister. It smells like fuel because when you kill the engine, the fumes rise up under the butterflies and into the hose, permeating it with fuel smell.
There's no possible way for fuel to get into that line unless you have a major issue. The line is under vacuum, not pressure. The only way for liquid to be introduced into that line is either a poor seal on the line itself, allowing liquid to be sucked in at the vacuum canister (assuming there's nothing else teed into the line), or the diaphragm is torn, allowing moisture to enter from the rear.
There's my tree fiddy.