Question Idle mixture setting on a Lycoming IO-360?

[Neal]

I have a modified IO-360 in my Carbon Cub FX-3 (363i CubCrafters calls it) and I'm curious about the idle mixture. In my 2021 FX-3 it needed to be leaned out on the ground and as the condition inspection checklist points out the RPM should rise 10-50 during lean to cutoff. In my 2023 FX-3 it seems the idle mixture is not rich nor lean but perfect. The RPM though does not rise and I'm not sure how important it is for idle mixture to be on the rich side. Seems having a correct mixture results in a better running engine and less risk of fouled plugs. I can certainly rotate the mixture thumb screw to richen it if people think it should be but I'm seeking opinions on idle mixture. Leave it as is or richen it?

 

[Cubonaut875]

I'm from the "If it ain't broke don't fix it" 10 RPM - 50 RPM is within the range of not significant figure in my stats courses mode of thinking. But to paraphrase McCoy "Bones" in Star Trek "I'm a Doctor Neal - not an Airplane mechanic!!" As a follow on question, how lean to you have your engine while warming up and initial taxi after starting?

 

[Neal]

The engine runs great, better than last in many regards. Not touching a thing.

I’m full rich and try to lean for a slight RPM increase during taxi but don’t get that on this plane usually.

Just curious about any desire to be rich of peak on the ground.

 

[Cubonaut875]

Mine seems to like being about an index finger first joint lean warming up. Do you have a Vernier? I speced one in the order sheet but when I came for my final build it was a standard mixture knob, as was the standard tailwheel not the Baby Bushwheel I specified. I told them to just leave it. Turns out it saved enough to pay the ferry flight and delivery.

 

[Neal]

No on the vernier. Heard not so good things about it such as it hits the fuel line coming down left side. Way too expensive too but that’s normal for CubCrafters.

Sorry to hear they couldn’t get your production order right. Beyond unsat!!