It wont' run the opposite direction unless you retime the flywheel. I did the same thing with a blower motor, was trying to start it backwards while having it mounted inverted, got gas on top the piston, and with the nissan starter that I have, bent the crank before I figured it out.

I have my echo chainsaw engine on a 24lb plane, has plenty of power to fly, not over powered, but flys very well. Steve