Exhaust Analyzer Results

73Swinger18 said
I took my Swinger w/318 to the carb shop to have them check the exhaust gases after a carb spacer change. The plugs look good and the car runs great. Not knowing much other than the basics of these numbers, does anything stand out to the trained eye? Two runs were taken at different RPMs as shown. Thank you.

To be honest, the numbers don't correspond to an Air fuel ratio if you look at a chart like the one that's in the article you linked to. Oxygen seems way high if there was no air pump. But there could be lots of reasons for that. Knowing that you put an open spacer under the carb makes me think this is hod rodded engine.

A really good tuner can take full advantage of a 4 or 5 gas analyzer, but it sounds like your people are a standard service station that is just using them for emmissions and troubleshooting stock vehicles.*

A spacer's effect on mixing and distribution will vary with speed and load. An open spacer is usually installed with the goal of improving wide open throttle in higher rpm (3000 up). Sometimes they can hurt distribution at low throttle and idle because of lost velocity. That's the only thing I'd be looking for on a steady state low rpm check like the two you posted. If you don't have a before and after, only a really smart cookie with lots of experience will be able to read much into it. However even if you don't, now you have a baseline.

The rpm of both runs looks to be at low throttle but above idle. On most carbs that's an area of the circuitry that's harder to adjust. It means fiddling with the idle air bleeds and sometimes the transition slot. Not that hard, but definately more than most mechanics get into.

*Examples:
Discussion of exhaust gas tuning tools.
A/F on a Dyno, Bruce "Shrinker" Robertson (archived post).
CO measurement, See also for Shrinker's comments on how CO readings are not directly accurate for useful for AFR.
Lambda [base reading WBO2 use for interpreting AFR] and emmissions.