From your description it sounds exactly the same as the Type 115 engine I have in my collection (pictures below), earlier style carb (no primer button), no tank, also no clue as to the original use.
Assuming it hasn't already been done, it will likely need a carb clean & rebuild, Webhead or Wallfish on here have new diaphragms for these, the original crumbly air filter foam should be removed/replaced too.
The original spark plug would have been a Champion UY6, if the cylinder has 10mm plug thread. Later engines used a 14mm thread spark plug.
David