Some O.S. 4 stroke engines will allow the carborator to be reversed so the needle valve sticks up, instead of down (side mount) or out the left or the right (upright/inverted). Make the hole in the cowl big enough so the needle and extension can be inserted after the cowl is mounted. More difficult, is the choke control. This exact topic is being descussed in the beginners forum, as we speak!