(1) Float type carburettors will only continue to function under negative g for a few seconds. Diaphram carbs solve this problem, but are usually only used in aerobatic aircraft due to the relative cost. SLMG also use diaphragm carbs because they don't mind being at a funny angle when the engine is folded away.
(2) Wet sump 4-stroke engines will, unless modified for aerobatic use, ony have an oil pickup in the base. Aerobatic engines have two pickups and a spring-loaded ball-valve that toggles between then (in Lycomings the prefix "AE" on the engine type signifies aerobatic mods). The snag with these oil systems is that the ball unseats and causes wild oil pressure fluctuations at low (0.5) g manoeuvres at low power - such as pitch changes in a long flight idle descent.
(3) Fuel pickups are usually only near the base (just above the sump) of a fuel tank. So if the above don't get you, you may well hit fuel starvation - typically after 30-40 seconds.
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