Re: 12.7:1 A/F Ratio
My bad, although the following excerpt from an SAE white paper from the 1999 journals is usually the norm for engine tuning:
Air/Fuel Ratio *- The ratio of pounds of Air to pounds of Fuel needed for combustion in an engine. Air/Fuel ratio is based on pounds of AIR to pounds of FUEL but carbs are metered (jetted) by volume so changes in fuel can change A/F ratios. A/F Ratios range from about 2:1 for NitroMethane to about 16:1 for gasoline, with 14.7:1 considered the stoichiometric or chemically correct ratio under perfect conditions with normal (non-oxygenated) gasoline. *Gasoline A/F ratios for best power tend to be in the 13.25:1 - 13.75:1 range.
As you can see there seems to be a few variables in the above excerpt, which when combined with the various dissimilarities between automotive engines (relatively low compression ratios, relatively low RPM range, much smaller intake tract (throttle body volume vs displacement)) and contemporary sport bike engines, may account for the higher performance gained from lower ratios on the Blade . . .