[niles]

O-2 sensor a very good and accurate way.
The old basic way is to do a plug check.
You have to drive the car for several second at the rpm your interested in; ie, 3000 light throttle on primaries, or WOT with a four barrels operating. Jam cluthe in, at the same time cut ignition off; roll to stop. Pull two plugs and carefully inspect. look at a good book for color pictures of what the porcelain looks like. It should be light brown/tan; if its black or sootie-too rich. white too learn. You can't slow down and drive back to garage before pulling plugs as the slow driving and idling for just a few second will mask the previously plug temperature.
grover