If it's running rich (the black smoke) it could be washing down the cyl walls I guess. Its an old engine that's why someone quit using it... Just buy oil by the gallon and remind yourself 'this is what it was really like in the old days'
DO the other stuff you mention in your first post and see what this does (after you adjust the carb) over the winter.
Is it a DD? how many miles a week does it see?
