I have a "few" of these engines and they like good fuel. Best results are a mix of leaded high octane with best pump gas you can get. I usually mix it about 4 to 1 pump gas to the good stuff. Using the unleaded stuff straight would not be my choice. It works in a pinch but these motors were meant to run with good fuel. The better fuel will even make the engine run cooler in my experience, and certainly make more power. I'll even throw a bottle of lead additive in once in awhile just for good measure.
wilma
ps: stay away from the aviation fuel it has a differnt specific gravity than auto fuel and may end of doing more harm than good. I'm no engineer but this was recommended to me by a friend who is a pilot.