10 - 16 AFR IIRC

I've leaned it out to 15:1 on a long highway cruise ( 3200 @ 70 mph) and got the 16 mpg's

it liked 12.2:1 at WOT on the dyno while I was testing for most power.

Whats nice is I was able to open the headers and the EFI compensated for the change - keeping it at 12.2:1