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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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Unfortunately we're getting a bit beyond my area of expertise here, but as I understand things, a good-running engine should have relatively little O2 in the exhaust. The exact figures will depend on whether the caburetors are tuned for economy, power, or some compromise.
Based on old smog test data for my car, I'd expect to see something like 6% O2, 10% CO2, and 1.4% CO at 1000 rpm idle, and 4% O2, 12% CO2, and 0.8% CO at 2500 rpm. Those figures were taken when the carbs were running a bit rich due to worn mixture needles. The ignition was a stock points system. (Aftermarket ignition systems could be expected to give better combustion at idle, and thus lower O2 and higher CO2 readings.)
(A fuel injected car will have much better figures as its computer varies fuel delivery so that exhaust O2 is at whatever near-minimum allows the other regulated combustion products to remain within requirements.)
As far as tuning using an O2 sensor goes, I don't know for sure but would expect that one would adjust each carb's mixture needle so you got the same results when both carbs were drawing equally as when either one was blocked off entirely. If that method didn't work, I'd want to see the same change in O2 when either vacuum valve was lifted the same small distance by a thin screwdriver or similar tool.
For mixture needle selection, I'd really expect the stock needles to be entirely adequate, and would change them only if the indications were that the carbs were obviously rich, or obviously lean, under some circumstances. As indicated in my previous post, the new needle choice would depend on where, precisely, things were rich or lean.
For damper oil selection, you'd want the mixture to go quite rich as the engine was accelerating, then taper smoothly to a normal fuel/air mix after a second or two at the new speed. A very slight single overshoot then single undershoot in the fuel/air mix during this 'tapering' period means you've reached the optimum damping rate for smooth engine response (which is not necessarily what's needed for greatest overall acceleration).
For a better understanding of the internal combustion process than I can provide, you might peruse the article at
http://smogsite.com/5gastheory.html .