I don't think this has been mentioned yet, but if you have ANY engine that backfires, make sure you check your prop bolts!

Backfiring will loosen the bolts quicker than anything except a wrench. I've seen first hand a prop kick completely off an engine, off the ground, and smacked the guy in the cheek. Luckily it had lost most of it's momentum before hitting him.

Just a word of warning, especially with this big of an engine.