Recently I put my car on the 4 gas analyser, and it gave me these results at idle:
CO2: 10.64 %
CO: 4.98 %
O2: 1.94 %
HC: 148 ppm
Lambda value: 0.93/13.7AFR
I have to mention that it concerns an older carbureted vehicle, so the tuning is rather usual. There is no EGR or secondary air injection, and the exhaust has no leaks. I am wondering how it is possible for the engine to leave almost 10% of the inducted oxygen unused while tuned rich. I would assume all the oxygen should be used in the combustion with this tune. Poor atomisation may cause poor combustion, but I wouldn't expect that to have such dramatic results.
The only other thing i can think of, is that intake air gets mixed in the exhaust at the time of gas exchange. But with these results, that would mean that the gas exchange here is extremely good. Is that assumption probable?
The valve timing is: