This is something I see very often when rebuilding carburetors. I call it "slime" but it's actually residue created by the solids that are distilled inside the crankcase recirculation bottle. It's easy to prevent. Simply empty out this bottle at the intervals suggested in the factory manual. Better yet, remove the bottle. This crap shouldn't be fed into your intake system.

The VB series carburetor with its labyrinth vacuum seal is the most susceptible to the harmful effects of slime. The labyrinth seal is a close tolerance fit.

Here's a particularly nasty example. That blsck goo is from the air filter box. It builds up in there thanks to the crankcase recirc system. Both the vacuum top's interior and its bronze bush need to be cleaned.

Another one. Really black, this stuff. How do you think the carburetors "like" this? Looks like it has been building up for a long time on this carburetor.

This particular carburetor was literally dripping with the stuff. I suspect the usual recirc issue was aggravated in this case by a fuel additive such as octane booster or Marvel Mystery Oil.

All the vintage Hondas that have this crankcase recirculation system are easily fixed, though on some models it's more trouble than it is on others. On this Gold Wing all you have to do is unplug the hose.