[IvanK]

Based on Torian's findings I went off and did some flight tests to determine Fuel Flow versus mixture.

I stand corrected based on Fuel flow tests CSU Spits and Hurris have correct Mixture lever orientation, however Levers are incremental and should be 2 position only. Boost Cutout requires some Leaning of the mixture to ensure smooth operation ... incorrect should be AUTO RICH.

Method:
10 min level Flight stabilised at 10,000ft on QNH 1013 +- 50 feet throughout.
Power Fixed at +2/2400RPM
RAD Full open (to provide constant test setting)
Full CEM
Fuel Set to 20% in FMB
Note via Tool tip Fuel Remaining at start and at 10mins elapsed on Stop watch.

RESULTS

Spit IA
Mixture Lever Full Back
Fuel Used over 10 min 8 Gall
Fuel Flow 0.8Gall min

Mixture Lever as far Forward as possible ensuring Smooth engine operation (about 75% forward ... any further forward resulted in rough running)
Fuel used over 10min 6 Gall
Fuel Flow 0.6Gall min

Conclusion Moving Mixture lever forward is Leaning mixture.
Mixture lever not 2 Position but incremental (WRONG)
Boost Cut Out req mixture lever forward of 1/3 to Full forward (Wrong)

Spit 1A 100 Octane
Mixture Lever Full Back
Fuel used over 10 min 8 Gall
Fuel Flow 0.8 Gall min

Mixture Lever forward as far forward as possible to achieve smooth engine operation (about 75% forward ...any further forward resulted in rough running)
Fuel used over 10min 7 Gall
Fuel Flow 0.7 gall min

Conclusion Moving Mixture lever forward is Leaning mixture.
Mixture lever not 2 Position but incremental (WRONG)
Boost Cut Out req mixture lever forward of 3/4 to Full forward (WRONG)

Spit IIA
Mixture Lever Full Back
Fuel used over 10 min 9 Gall
Fuel Flow 0.9 Gall min

Mixture Lever forward as far forward as possible to achieve smooth engine operation (about 75% forward ...any further forward resulted in rough running)
Fuel used over 10min 7 Gall
Fuel Flow 0.7 gall min

Conclusion Moving Mixture lever forward is Leaning mixture.
Mixture lever not 2 Position but incremental (WRONG)
Boost Cut Out req mixture lever forward of 1/3 to 1/2 Full forward (WRONG)

Hurricane I ROTOL
Method Fuel Feed Main Tanks. Fuel used Total read from both Left and Right Tanks based on assumption that fuel feed simultaneously from both Left and Right tanks.
Mixture Lever Fully Back
Fuel used over 10 min 10 gall
Fuel Flow 1 gall min

Mixture Lever forward as far as possible to achieve smooth engine operation (about 75% forward .... any further forward resulted in rough running)
Fuel used over 10 min 6 Gall
Fuel Flow 0.6 gall min

Conclusion: Moving Mixture lever forward leans mixture
Mixture lever not 2 position but incremental (WRONG)
Boost Cut Out req Mixture lever Fully back (CORRECT)

Hurricane I ROTOL 100 Octane
Method Fuel Feed Main Tanks. Fuel used Total read from both Left and Right Tanks based on assumption that fuel feed simultaneously from both Left and Right tanks.
Mixture Lever Fully Back
Fuel used over 10 min 10 gall
Fuel Flow 1 gall min

Mixture Lever forward as far as possible to achieve smooth engine operation (about 75% forward .... any further forward resulted in rough running)
Fuel used over 10 min 9 Gall
Fuel Flow 0.9 gall min

Conclusion: Moving Mixture lever forward leans mixture but not as much as in 87 Octane ROTOL Hurricane.
Mixture lever not 2 position but incremental (WRONG)
Boost Cut Out req Mixture lever 3/4 Forward (WRONG)

FIXES REQUIRED
Mixture lever should be two position only not incremental
Full Back = AUTO RICH (automatic altitude compensation in rich schedule no Boost restrictions)
Full Forward= AUTO LEAN (automatic altitude compensation in weak schedule Boost restrictions apply)

2 PITCH TESTING IN COARSE
Slightly different method. Set +2lbs Boost Coarse pitch and accept RPM achieved, all other aspects the same as in CSU tests.

SPIT I DH COARSE
Mixture Lever Full Back achieved RPM 2000
Fuel used over 10 min 6 Gall
Fuel Flow 0.6 Gall min

Mixture Lever full forward achieved RPM 2150
Fuel used over 10min 8 Gall
Fuel Flow 0.8 gall min

Conclusion Moving Mixture lever forward is en riching mixture. (WRONG)
Mixture lever not 2 Position but incremental (WRONG)
Boost Cut Out req mixture Full forward (should be Full Aft if orientation is correct)
Richer Mixture results in increased RPM for a given Boost

Hurricane I DH
Mixture Lever Full Back achieved RPM 2000
Fuel used over 10 min 6 Gall
Fuel Flow 0.6 Gall min

Mixture Lever full forward achieved RPM 2100
Fuel used over 10min 8 Gall
Fuel Flow 0.8 gall min

Conclusion Moving Mixture lever forward is en riching mixture. (WRONG)
Mixture lever not 2 Position but incremental (WRONG)
Boost Cut Out req mixture Full forward (should be Full Aft if orientation is correct)
Richer Mixture results in increased RPM for a given Boost

2 PITCH FIXES REQUIRED
In both Spit and Hurri DH mixture lever orientation is WRONG and needs to be changed
Lever back should be AUTO RICH
Lever forward should be AUTO LEAN
Mixture lever is incremental should be 2 position only

NOTES
AUTO RICH provides automatic altitude compensation on rich schedule without Boost restrictions
AUTO LEAN provides automatic altitude compensation on a Lean schedule with Boost Limitations.

In AUTO LEAN engine Boost limitations should be
Hurricane I, Spitfire I +2.5lbs Boost
Spitfire II +4lbs Boost

EDIT: All RAF fighters tested.