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Modern marine 2-strokes are direct injected and are much more efficient than carbureted or fuel injected 2-strokes. In a direct injected 2-stroke, fuel is injected right down at the piston as it closes the exhaust port, so very minimal (if any) fuel escapes out the exhaust. Also, in a direct injected 2-stroke, oil is not mixed with the gas, as it is contained and circulated much like a 4-stroke car engine.
Power curves can be tailored for a broader torque range by using (what they call in motocross) a "Power Valve". Its basically a valve that alters the diameter of the exhaust port, which in turn changes the power characteristics of the engine at certain rpm's.
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