The carburettor on the Gipsy Queen 70 MkII operates schedules Lean mixture below a given Boost/RPM threshold and increasingly Richer mixtures above.
We used to climb at +2 Lb / 2400 RPM (34" for the Yanks), and had a lot of Cylinder Head problems, as this was the upper limit of the Lean range. Upon increasing Climb Power to +3 Lb / 2600 RPM, the problem disappeared.
Hope that that helps.
Regards,
Old Smokey