[Fot] Curious Air Fuel Ratio numbers

[Jim Gray]

Greetings FoT

I'm tuning a fresh motor and am getting some strange numbers on my AFR gauge
( autometer wide band ) 

with Mikuni HSR45 carbs. 

I have a very different engine than last year so I'm starting from scratch
on my jetting this year. 

I just put in a fresh 02 sensor and am seeing AFR of 9.4 at 4k RPM cruise
and WOT from 3K to 6K.

However, when I lift from 6K to zero throttle the air fuel goes to 10:1,
11:1 and 12:1.

The plugs have some color but nothing indicating a mixture that rich. I
haven't done any proper full throttle 

shut downs on the plugs yet, just trying to get closer with AFR's & EGT's

Exhaust gasses haven't gone over 1200F yet. Since the car is registered for
the street I'm just trying to get 

a tune that's close before I get it the dyno for the " real tune "

I haven't ruled out a faulty gauge/afr reading either. I've had new parts
let me down before.

Just wondering if anyone has seen a mixture go lean after throttle lift.
Seems kinda bass ackwards.

Thanks as always,

jim g