I don’t believe ‘Miss Shilling’s orifice’ aided inverted flight.

Didn’t it just temporarily maintain flow in the bunt, nose forward, negative G manoeuvre, which had previously starved the earlier carburettor variants of the Merlin. A manoeuvre picked up by the Luftwaffe to advantage.

Mark

That`s right, as far as I am aware, none of these aircraft of any nationality were designed to fly inverted as such. Neither the oil pressure or scavenge systems will work effectively when inverted.

Merlin SU carbs after the Battle of Britain era had a modified float needle valve to restrict maximum flow, Miss Shilling`s orifice being an interim field mod.
Some single-speed Merlins with SU carbs also had a diaphragm-fed float chamber for this reason.
According to the relevant manuals, the diaphragm-feed allowed both inverted flight and negative G manouevres, but I still say the lubrication system would be pretty lacking!

Pete