I like and use 14.3 to 15.3 AFR at idle on the fuel and altitude where I live, that being said the plugs at 11.8 to 12.5 at idle will be very black, not good A lean mixture burns much hottor and is more efficient, not all motors like rich mixtures, most Chevys do Lots of ways to tune On the WOT try using some 1000 grit sand paper or some scotchbrite on the bottom step of your metering rods to enrichen it, measure it first and often, shoot for .002 smaller at first Make one jet size change bigger on the secondarys also Tune it until you like it, don't be suprised if you get it to lean or to fat before you have it perfect Watch the sparks plugs while tuning it, all 8