Flipping the prop around won't help. I sure wish it did. You have to buy a pusher prop to do the job. Also make sure the label is facing forward on your prop. Or that prop Leading edge meets the air. You can probably use an 11x7 or a 12x6 for that engine. Tower hobbies sells various pusher props in the size you'll need.
http://www2.towerhobbies.com/cgi-bin...=++&search3=Go
Dan