Dave:

""How steady is your AFR at highway cruise?""
- At a steady throttle, the reading is very smooth (exp: 14.4-14.6) and I take the average to write down. I have seen a larger swing but that was when I was running leaner on the transition circuit. Overall, I would have to say that the guage reading is smooth. Sorry that I can't help you out on the guage swing, but do you have any air leaks on the exhaust "before" the bung?

""Do you use vacuum advance?""
- No. I have a FBO distributor and he plugs them up.

""Previously I had convinced myself that the motor was only getting fuel from the transition at 3K cruise, but your experience made me question that. I came to this conclusion because changes in the main jets didn't seem to be having an effect on the cruise AFR, but in hindsight expecting to see the effect of a couple jet size changes with the AFR swings that are occurring is a little foolish.""
- I can't give you an answer but I can tell you that I read an article to help find how to tell when your mains are coming in. The answer was to raise the main jetting by at least 4 sizes so that you will see a dramatic change in A/F ratio once you hit the mains.
I have found in reading about different brands of carbs, that each manufacturer may have a different opinion on if the carb should be running on the main circuit or on the transition circuit at cruise. My QF carb appears to be running on the transition circuit at cruise.

Doc:
I run the FAST #170634 analog unit. My exhaust is setup as two separate sides (no h or x pipe) and each side has a bung in the header reducer. I am only running one sensor and I have only tested it on the drivers side.