Setting idle mixture

[00Dan]

I’m familiar with the trial-and-error process of setting idle mixture and speed by pulling to cutoff and observing RPM rise. Can idle mixture be set by fuel flow? If it’s possible it seems it would be easier than sawing at the mixture trying to find the sweet spot.

I’ve dug into the Lycoming operator manuals and haven’t found any specifications for fuel flow at idle.

 

[Ralph Inkster]

Never heard of that approach.

I do know there is some variance in Idle mixture settings dependent on airport elevation so some generic fuel flow figure would also have to vary.

 

[rv8ch]

Are the FF sensors we use accurate down to 1 GPH? Not sure, but at idle (650-700 RPM) I typically see about 1.3-1.4 GPH (IO360/AFP FM200/pmags).

 

[622BH]

AFR Sensor

If you install an Air Fuel Ratio (AFR) Sensor system in your aircraft you can adjust your idle mixture using that for a desired AFR for your airport's altitude.
It's best if you can set it to (at) sea level then you would have sufficient adjustment for higher altitudes. If you set it for (at) a higher altitude airport, you may not have sufficient enrichment adjustment for those airports lower than yours.