15.0 mpg to 21.6 mpg!

crackedback said
JMO

Don't tune to a number, tune for performance/mileage. That 12.2 number is only a suggested point and will vary greatly depending on engine, fuel, load and other factors.

For WOT, take it to a track and tune it for best MPH. That is where the engine is happiest at WOT. If it happens to be 12.2, OK. Likely won't be 12.2.

This should be a quote that's posted at the site signiture. I have always said, and always will say, numbers just get you in the arena. All the fine tuning, wether it be initial timing, full timing, jetting, and even carb cfm, should be determined by what the engine likes/wants.