Edelbrock Carburetor tuning question...

FWIW, just an observation.....I have been getting back into the carb scene after an absence. Reading the plugs with the new fuels just does not seem to work like it did 20+ year ago. My son's 340 plugs (with HEI) come out scarily clean no matter what. But we put an AFR meter on it a week or so ago, and it is overall running rich at light cruise and lower RPM's (when it is on the idle circuit) and the highest AFR we see is about 16 at 55 MPH, going down a slight grade....where I would expect it to be a bit lean. But the plugs show no color on the porcelain.

Until I learn to look waaaay down at the porcelain base and read plugs, I am not going to trust my old plug reading for tuning with the new pump fuels. BTW, we are using Shell Premium.