There is good write up on the VRO system here
One problem that can occur, and I experienced with mine: Perforation of the yellow diaphragm in the picture. This allows oil to dribble into the upper fuel chamber.
(yes, we did the the vacuum and airtightness test recommended and both engines passed).
My engines were averaging 30:1 as result (should be much less with a VRO - that's the whole idea). I had clouds of smoke, hard starting, oily carbs, sooty plugs.
Two new pumps would have been very expensive ($500 USD ea from memory). So I disconnected the oil system, removed the VROs, disconnected the no oil alarm and replaced with two aftermarket fuel only pumps. Yes. that's right - so many people remove VROs, there are aftermarket, bolt on petrol only replacement pumps. Obviously from that point on I ran 50:1 premix.
Guess what ... all the issues disappeared and I gained two storage compartments on the boat (where the oil tanks used to be). That was ~5 years ago and I've never looked back. Engines start easy and run all day without issues.