Mixture control Spit?

[Sokol1]

You already check "Complex engine management" in Options > "Realism"?

Mixture lever work in all Spit versions, but have only two positions "Rich" or "Lean".

From TF wiki manuals:

CARBURETOR MIXTURE

The engine is equipped with a carburetor which allows the pilot to select either 'Rich' or 'Lean' mixtures. 'Rich' mixture is used in all normal situations, takeoff, landing, climb, combat. 'Lean' mixture is only used to conserve fuel in level flight Cruise settings, and only when boost is set to '+1' or lower, and rpms to 2600 or lower. Use of 'Lean' mixture setting at higher rpms or boost will result in the destruction of the engine.

In practice dont worth change mixture adjust.

In Hurricane (and DH-82) mixture lever movement depend on throttle position.

Sokol1