[THEFERMANATOR]

For that size engine, you won't see much difference. It takes X amount of fuel to make Y amount of HP, and Y amount of HP to go Z in speed. It's not like you're comparing a small 2 cylinder kicker to a 4 cylinder primary pusher engine. I doubt you would see a huge difference if both kickers were propped the same. And I would say prop choice plays a bigger role in fuel consumed than the difference between a 9.9 and 15.