I just completed mine. For a 2 stroke, you want to line it up with the horizontal line and the line that is at a 45 degree angle on the firewall. You motor will be mounted at a 45 degree from sideways with the jug pointing in the downward 45 angle. Attached is a pic you might get an idea of. The angle is for muffler to dump out the bottom. I installed an O.S. 50sx on mine. Sweet flying plane. With the 50 on, it will knife edge pretty good, but wants to pull towards the belly. the instructions say to insert some washers under the motor mount for some up thrust. I didn't do this and going to before the next flight. Still don't have calon on though...