Merlin negative G cutout too quick?

[Crumpp]

an inverted flypast

It was a positive G maneuver most likely and certainly did not have a float carboretor. AFAIK, Spitfires were not outfitted for inverted flight.

Float type carburetor's are not capable of inverted flight as fitted to the Merlin.

When a carburetor is inverted, it can no longer meter fuel, and the float rises and cuts off the incoming supply.

http://www.airspacemag.com/how-things-work/upside.html