As far as your fuel straight to the curb from the tank, that sounds like a gravity fed system, so no gas pump is needed.
I am not sure how helpful this will be as I'm new to Small engines as well but with a car when you have that happen it's your head gasket or lower gasket that needs replacing. So when you emptied out gas and oil did you take it apart and replace the gasket to keep the two fuels separated, if not you will need to do that.
Do some research and look for a gasket before you attempt to do it.
Once you have the gasket make sure you clean both sides when you separate it very thoroughly before putting the gasket in and back together.
As for the black smoke that sounds like the oil gas mixture blowing off in the carburetor which should be cleaned when you take care of the gasket and then it might go a couple times after but should disappear and not be blowing black smoke any longer.
I hope that this is helpful, good luck