The efficiency of the engine will increase if you lower the temperature that is known as "TL". If your bike was the most efficient engine ever made, thus a Carnot Engine, and the top temperature reached was "TH", then the efficiency would be:
1-(TL/TH)
That's assuming everything went perfect. So by lowering the "TL" or keeping your engine's ambient temperature/surroundings cooler, your engine would theoretically make more power, or be more efficient.
Using the same logic, raising the combustion temperature one or another would increase the efficiency as well. Like increasing the compression or in a very small way, using hotter burning spark plugs (theoretically speaking).
Too bad the Duc isn't quite a Carnot.