The serial number makes your outboard a fairly early 1923 model.The “barrel shaped thing under the gas tank”is the muffler can.It and the two exhaust manifolds on each end make up the exhaustThere is no air filter,only a carb with an L shaped air horn (often missing).The propeller for the early A models are different from the later models.Jon Koranda is the group leader for the A model Johnsons and he may be to help with parts.
