I ran my duster 518 motor at or above 14.3 to 15.2 AFR at part throttle up here at 3500 Ft above sea level on my Innovate LM1 with the LC1 conversiion to dual wide band I did run a cooler plug than most, Autolites AR3911 and AR3910, I also ran both the Champion RC12YC and the RC9YC, the motor ran well with all of them I had it at between 12.8 to 13.5 AFR at WOT with the six pak and the single 1050 CFM Dominator carbs. I tested, I had issues early on with inadequate fuel supply(10 micron fuel filter between the tank and the pump )the motor would leave the line at 14.2 AFR and cross the finish line at Bakersfeild(in really bad weather conditions) at 15.8 I got lucky and didn't hurt it, don't try that yourself Tune it until you like it, lean it down until it feels bad, richen it up until it feels bad again, find the sweet spot you like Then look closley at the plugs for the part throttle driving and put in several new plugs when you go test the WOT runs IHTHs