Quote:
Originally Posted by Ryland
Motorcycle engines also tend to be air cooled (again, not always the case) and with an air cooled engine it's best to run rich as fuel as a cooling affect.
Motorcycle engines also have very short intake runners, there have been a hand full of people who have made longer intakes on motorcycles and seen low end torque increase and gas mileage increase but they take up space so they are not often used.
But what it boils down to is that even tho a motorcycle engine is a small displacement engine there are a lot of compromises that are made to make it smaller, lighter and produce more HP for the size/weight.
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I think that may be why even the water cooled engines tend to run rich too. My water cooled motorcycles won't stay warm in temps below about 50-60°F. At that point, there is so much airflow past the engine that the radiator is uneeded at highway speeds.