There is a common misconception about the fuel thing. Premium fuel burns slower than Regular, not hotter or cooler. That's why it can give more power in an engine that has been designed for premium, as it ignites it will expand and apply even force as the piston moves down. Regular may be burned up before the piston is all the way in it's downstroke and a "ping" or "knock" is the result. What does determine the temperature in the cylinder is the air fuel ratio. Most engines work the most efficiently and last the longest at a 14.7 to 1 AF ratio. That number is based on maximum power along with maximum longevity.
The first thing to do is run that engine the way it was designed to run. Regular fuel (non-ethanol preferred), correct carb settings, straight 30W oil, correct spark plug, and points at .018.
I have a Sun 500 that I've used to set carbs by AF ratio, it's the only way to get one perfect.