You don't need severe neg. G to starve a Shrike of fuel, anything less than 0 G can do it, and the leaner the mixture the apparent quicker the onset of fuel induced hesitation, returns with positive G.
The culprit is I believe the fuel vapour separator located on the firewall of each engine which has a ball float of some description inside. It is not unheard of (not common either) for a sudden gust to stick this ball float at the top of the vapour separator and stay stuck until removed or tapped with a hammer.
A good reason to stay within the positive envelope of the Shrike at least with the 540 E1 B5's which are incidentally normally aspirated and fuel injected.