The Ryobi 31cc I did came out of a string trimmer and was inverted in the trimmer so thats the way I'm mounting it in my airboat . It runs great and it will lower the weight closer to the top of the hull . I don't think it makes any difference where the bulb is . The carb on the Ryobi is in the back and I just removed the primer bulb and plugged the line at the carb .