I spent some time with the Tod at Continental on Friday, tuning the carbs on my P6 cam'ed (290 duration, high overlap) 308. This car is also fitted with a wideband A/F sensor (fitted post header, pre-muffler). The AF sensor has been calibrated to within 200 feet of the altitude here in Chicago so I am confident of its accuracy. Being a 77, it has no cats. After sync'ing the carbs, dialing in the mixture, driving the car to get it good and hot, and then re-doing the mixture (and re-checking the air flow), all per "the book", we are finding it wants to idle best and pulls best low down while recording a very rich mixture (11.5 or 12:1 on the A/F readout). Leaning out the mixture to the "normal" range (say 14:1) causes additional drivability issues. For any given A/F mixture input, high overlap cams will, other things being equal, lead to a richer mixture being recorded by an A/F sensor due to the greater presence of unburned fuel in the exhaust. A smaller overlap reduces the unburned fuel/leads to more complete combustion of the fuel and hence a cleaner exhaust. This clearly was one (the?) impetus for the "softening" of the cam profiles of the later carb'd cars as they were "tamed" to meet emissions requirements. My question is therefore two-fold: 1. I assume the effect of the cam overlap on recorded A/F mixture will be greatest at low rpm/idle. 2. At mid to higher RPM (say 3000 up), with the engine acting more like a pump, the A/F measurement versus a "normal" target (like 12.8 or 13.2, for example) will have more salience than at idle. Any thoughts?