Engines 101 or what I wished I asked my Thermo prof: Confirmed with a 5 Gas Analyzer - The CO setting on say an injected 308 or 512 works out to be ~2% for a pretty efficient stoich value of ~14.7 A/F ratio. But on an older hi-perf engine like a Dino, or 275, at 14.7 A/F, the CO is ? (like ~5+%). Does this sound right, and if so, any good explanations?
You are leaving the word "idle" out of your question. With CIS, the atomization of the fuel at idle (when the air velocity is quite low) is still pretty good; whereas, with a carb, at idle, the fuel is just dribbling in in big drops -- consequently, the carb idle spec needs to be a little overly rich to prevent occasional lean mis-fires. A carb set for 5~6% CO at idle probably won't be running quite that rich at cruise, but it's the variability in a carb that necessitates running richer overall than an injected set-up (i.e., stoichiometric isn't a different thing for carb vs injected, but, with less variability, a system can run closer to stoichiometric without going under and lean mis-firing).
Sure -- although the guys reporting only 7~8 MPG in a 400 must have something else not quite right with their fuel delivery IMO. The civilized world was very lucky that an IC engine could run well over a very wide A/F range (even if the emissions weren't great). The early, early carbs were truly primitive -- fuel dripping on a wet sponge
