Sure. Please provide source material that will save us the effort of guessing.
Actually the Spitfire I Pilot's Notes quote 89 imperial gallons per hour all out at FTH, which is only about 1.5 gallons/minute.
You might see 3 gallons/minute from a Merlin 66 running at +25 psi, since it produced roughly double the shaft horsepower; but that's very much a horse of a different colour. Actually I seem to recall that somewhere I've got the accurate figures for the mighty RM.17 SM engine which was of course the thirstiest Merlin of all; but they're not at university with me.
Why exactly does the absolute flow rate matter? We care far more about dimensionless parameters such as FAR than we do about the absolute rate of fuel flow, which serves merely to tell us that
Big Engine Is Big...
Actually, if you want to get into analysis, the Merlin should be inherently more forgiving of the failings of carburettors than a more modern naturally aspirated GA engine because the supercharger both vigorously mixes the charge and heats considerably. Therefore the fuel is considerably more likely to be fully evaporated and homogeneously mixed than would be the case for a naturally aspirated engine.
I would submit that the Merlin was not especially delicate; whilst its reliability was imperfect, especially during its early life, it was considerably better than many other engines (e.g. the Rolls-Royce Vulture, almost anything ever made by Napier, many early Bristol sleeve valve engines etc).
The early ramp or "penthouse" head engines certainly had trouble passing type tests, but of course we're not talking about them in this context, since all of the aeroplanes we're interested in are fitted with Merlin II or later engines.
How exactly do you think anything with a carburettor could be "instant"?
The carburettor is quite some physical distance from the cylinders. The flow velocity in the induction system, other than at the supercharger impeller tip, is subsonic and thus decidedly finite. It therefore obviously takes some time for any leaning of the mixture at the carburettor to impact upon the mixture at the cylinders and thus the engine shaft power output.
So even if the leaning of the mixture at the carburettor was instantaneous upon reduction in positive g, any effect upon the engine clearly could not be.
But of course, the impact of g load upon the carburettor could not be instantaneous because it is caused by physical displacements brought about by inertial loads. So obviously there is a time lag involved here as well.
Actually, inherent time lags are one of the (many) arguments raised against the carburettor, especially for automotive applications where swift throttle response is considered important.
Did you read the accident report I posted, which contains considerable information on the history of negative g cut behaviour in the Merlin?
Did you watch the video I posted which shows the actual phenomenon in flight? You can quite clearly see and hear the lags involved.
Here is some more source material:
http://www.flightglobal.com/pdfarchi...%20carburettor
http://www.flightglobal.com/pdfarchi...%20carburettor
http://www.flightglobal.com/pdfarchi...0-%202734.html
There's probably a cutaway of the SU carburettor out there somewhere on the internet, just waiting to be found... I've almost certainly also got one in my library at home, but that's several hundred miles away...