Some more reading, note the Yankee Z ad near the end. --- https://books.google.com/books?id=efkDAAAAMBAJ&pg=PA7&lpg=PA7&dq=upswept+2+stroke+jr+exhaust&source=bl&ots=GeneA1IeFa&sig=ACfU3U0XbxhRH-agiOtiMye24GIfA115AA&hl=en&ppis=_e&sa=X&ved=2ahUKEwjCjorzr8rmAhUEP6wKHW7nDl4Q6AEwGHoECAoQAQ#v=onepage&q&f=false