[IvanK]

Greetings Banks. Good snippets in para IV excerpt especially.

These are however from the Generic or Pilots Notes General (AP2905) so arn't specific to the Spitfire installation. Though I do see your point there. I am trying to find these sections in my copy of the AP2095 (2nd addition dated April 1943) but so far cant... I guess thing s changed between the early and second versions.

Same goes for the discussion of excessive rich mixture for Take off boost its a generic statement. In short I believe it a discussion on Mixture use versus Boost but not an indication of a specific systems design.

Reading the Spit II notes I see what you are saying about 2 systems. The manual states in the take off section that max boost can be obtained by pushing past the gate no mention is made of the Boost Cutout switch in this circumstance. So I agree with you here and I was incorrect. So the gate gives +9Lbs. Pushing past the gate on Takeoff will give you +12.5Lbs but with ABC still operative. In Flight however as you said Boost cutout (ABC now not operative) gives you only +12Lbs ... so there is still something limiting you to +12Lbs .. (The mod driilled Bleed holes in the ABC I presume ?). What would happen say at 2000Ft if you simply pushed full throttle past the gate +12.5Lbs or +12Lbs ? Why this diff between +12.5Lbs and +12lbs ... no idea. I need to do some more homework here.

I will delve into the Merlin manuals and the various early Spit maintenance manuals to see if there is anything more specific.

Of note is the Spit II Merlin XII throttle system is different to the Spit MK I Merlin II/III system

What manual is the last jpg from the one with the line drawings ? This is dealing with a 2 speed supercharger running MS and FS gear (file name implies Merlin XX) , its not relevant to the Merlin XII or II or III as fitted to the Spitfire I and or II.