The main jet is in the way of the right rear screw. To mount the engine, you have to put that screw in first, and partially tighten it, with the strap on. Insert the motor, and then the front screw. You will see how far you must tighten it to make the strap level or even when you tighten the front screw. It is trial and error until you get the rear screw tight enough that when you tighten the front screw, the motor is secure. The muffler needs to be removed to install the left rear screw. You are lucky, the mount "holds" the nylock nuts in place for you, saving you some time there. Use caution when removing the muffler so that you don't ruin the gasket. I have 2 of these planes, they work pretty well.