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With the fuel injected models, the O2 sensor is going to automatically, add more fuel with more air. It´s gonna automatically, keep the fuel air mix fairly constant, and at the same time adjust ignition timing. The only time you´re gonna run out of fuel is at extreme RPM´s.
Caburated models (regulated) are pretty much the same. The carb is gonna keep a pretty constant air fuel mixture. Unregulated carburators might benenfit from a slightly larger main jet, then again may not. More fuel doesn´t neccesarily translate into more horsepower. A slightly lean motor, produces more horses than a slightly rich motor. Though a slightly rich motor often lasts longer and is less prone to detonation.
In my experiance a better flowing intake, helps the motor to rev a little faster, but most of the benefit is noticed at higher RPM´s.[addsig]