[JudgeMingus]

It should be noted that even direct injection does not make the engine totally immune to negative-G problems even though it does allow the engine to run under a short period of negative-G.

There is still the matter of supplying oil to the engine and fuel to the injector/carburettor - generally these are drawn from the bottom of their respective tanks. Sustained negative-G will at some point cause supply reduction or interruption and thus problems with engine starvation or damage.