This is because the spit I and hurricane I are carburated engines. Pulling negative G's starves the engine of fuel causing it to die. Later fuel injected engines due not suffer from this. Saw an intervue with Gunther Rahl IIRC where he said if you had a spitfire on your six to push the nose over and the spit could not follow. I'm sure they got a rude surprise when the fuel injected spits showed up and followed the negative G manuver.
As I learned one day, later Spits are also carborated but they placed a diaphram into the carborator to keep the fuel from flowing back out.
From
http://www.spitfiresociety.demon.co.ukOne of the great problems as discerned by pilots was the tendency for the carburetted engine to cut out under negative 'g'. Luftwaffe pilots learned to escape by simply pushing the nose of their aircraft down into a dive, as their fuel- injected engines did not cut out under these circumstances. Many authors have criticised this aspect of the Merlin design. In reality, like most engineering, it resulted from a design compromise- the drop in temperature developed in a carburetor results in an increase in the density of the fuel-air mixture when compared to that of a fuel injection system. As a consequence the Merlin produced a higher specific power output (horse power per pound) that the equivalent German engine. It was felt that this gave a higher power to weight ratio for the fighter and (rightly or wrongly) that this outweighed the disadvantages. By 1941 Miss Tilly Shilling in Farnborough had developed a partial cure for the problem. A diaphragm across the float chambers with a calibrated hole (the infamous "Miss Shilling's orifice"!) allowed negative 'g' manouvres, and was fitted as standard from March 1941. Sustained zero 'g' manouvres were not sorted out until somewhat later. In 1942 an anti-g version of the SU carburetor was fitted to single and two-stage Merlins. 1943 saw the introduction of the Bendix-Stromburg carburetor which injected fuel at 5psi through a nozzle direct into the supercharger and was fitted to the Merlins 66, 70, 76, 77, and 85. The final development was the SU injection carburetor which injected fuel into the supercharger using a fuel pump driven as a fuction of crankshaft speed and engine pressures, which was fitted to the 100 series Merlins.
