Gonna check my KE jetronic manual at home but what is the optimum AFR for running your car and what is the limit for best performance??

Thing is I get my new wideband innovate AFR guage delivered tommorow and need to know what to check for once its installed!

Also I need to sort why on my current narrowband gauge does it trop off way lean when I take my foot off the accelerator under boost?? or normal driving?