What kind of carb is used? Power valve size? Remember plugs are the soldiers on the front line and the only ones that will truly tell you what's happening. Like Andy said you can't always trust AFR meters. Plugs you can always trust. What heat range of plug? Does the carb have a secondary idle setting screw? Front and back should be set equal. Remember KISS keep it simple before totally changing everything out of whack in the carb. I see it all to many times. 02 says one thing plugs tell a whole other story. Just the angle and position of the 02 will change the readings. It's not a mild cam anymore which really changes the effectiveness of the 02 metering. Most turbo EFi that use 02 tuning run shorter duration much wider LSA which will give much more accurate readings. That's why even over 1000HP boosted cars idle much smoother. The 5000hp stuff is a different story again. . Are you trying to get fuel economy,go fast or somewhere in between?