What A/F ratio you running?

How in the world are you guys getting 14-15 afr's at idle & able to keep the engine stilll running?!?!?!? neatther one of my darts (one is a mild but strong hi-po 273 4-speed. The othere is a nasty 340 automatic with 3800 stall) any leaner than 13 both engine's start to miss & can watch vacuum drop on gauge even before they start to miss. Rule of thumb for carburetor motors the highest vacuum reading usually is around 12-13 ish. My cruise is around 15 & w.o.t. 12.8 -13.1 273 ides @ 750-800 with 15.5 steady vacuum. The 340 is about @ 1000-1100 with a steady 11 vacuum.