Well, every time I've gone even a hint negative in a non-injected aircraft, the engine has obliged by immediately going fairly quiet. Normal power is restored immediately as soon as positive G is restored. (Throttle closed as soon as it dies, and smoothly opened again as required.
Even the aircraft I did an aero rating in (the mighty 152) was not supposed to be operated inverted. The oil pressure drops after a few seconds. At that point, positive loading should be restored PDQ. It's not terribly critical, as it's not producing power at the time. So my instructor informed me. But you don't dick around gliding inverted for, say, half a minute at a time.