Re: what did you do to your motor bike today?
That sounds like an exhaust gasket leak. The exhaust can spew out black oily gunk if the gasket is leaking. If the head gasket is leaking it will spit out a fine oily mess on the outside of the engine that can turn black after road crap sticks to it. The only black you'll see is the first 1/2" or so directly around the leak itself after you remove the cylinder head. Also a head gasket leak will cause a lean condition and the engine will run wrong.
"It's a chinagirl. It's a sometimes fun little engine that often will break your heart. It's disposable.
Does not come with a fortune cookie."