Thanks James..
Richard..the problem with that is if the cavitation occurs before the fuel pumps, turning them both on would make no difference - they would both suck air...(often the vapourisation can occur before the pumps).
Or even vapourisation is occuring at the pumps, there would be a lot of air (vapourising fuel) in this area so neither of the pumps would be able to get good suction (as you know it's actually only quite a small area in the pump housing and they are basically under the same heat conditions).
When I did my research into this (after my incident) I found that sometimes mogas can boil as low as 40 deg (c) at around 8-10,000 feet - depending on the fuel, line pressure etc. This is made worse with suction, creating lower pressure (reducing the boiling point further). I am thinking the best 'cool' place is in the cabin down low somewhere (positive gravity feed, fuel can never boil here). This then ensures positive fuel pressure in your fuel lines in the hot areas of your fuel system before the engine (not suction).
The Rotax pumps are reciprocating pumps that spin at very high speed - once they cavitate, it's not easy to stop them - it really needs fuel to be 'pushed' into them. That's why I used diaphragm pumps (facet pumps) to kind of push the fuel to them. We also made sure that with the fuel system running on the ground (engine off) the 2 facet pump-assembly had enough pumping power to ensure positive pressure (above and beyond the 2 x Rotax pumps).
I am not sure if I got any photos of my setup (and it's in an awkward place to access), but I will try and sketch it up and post it.
