AFR/CO%

[73Swinger18]

I wanted to verify the AFR on my 318 so I took it to a smog shop and asked them if they could take a quick reading. We threw the sniffer in one of the pipes and it read 5% CO at 750 RPM and 2% at 2,000 RPM. They didn't charge me for it which was nice. I'm wondering if this would be an accurate (or close enough) measurement of my ratio. Below is a chart I found with some guidelines for CO%. The base ring on my plugs have a full turn of color with no soot, but the readings seem a bit rich. Not sure if I'm going to leave it or try to lean it out some. Thanks for your input!

Notice they list "typical" and "well tuned"

 

[73Swinger18]

I dropped two sizes on the primary jets and went back to that shop today, but they were closed. We'll see what it does to the numbers.

 

[73Swinger18]

I found this CO% to AFR chart. I'm wondering if this chart is valid with all testers, or only the specific manufacturer who published this chart?