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I've been wondering that too. They don't use them on Cessnas.
The standard 750 FWF kit that Jabiru USA supplied did not include a boost pump. I flew hundreds of hours without one and had zero issues. Later, purely for experimental curiosity (and to gain a mixture control), I switched to the Sonex Aeroconversions "AeroInjector" throttle-body carb. (Despite the name, it's just a carb - not a fuel injection!) The AeroInjector TB carb runs best on gravity feed, so typically the Jab's mechanical fuel pump is deleted and the mount blocked-off. I now have 175 hours on the AeroInjector running strictly on gravity feed only and it works great in all normal flight attitudes and fuel tank levels. So, all that is to say that I don't think an electric boost pump is necessary and just adds another layer of complexity - and remember, gravity is always "ON!" ;>)
I don’t have a fuel pump on my 750. I have the Continental C-90 engine with a MA3-SPA carb. It’s flown for 7 years and done fine. Simple is good!
Only have 25 hrs so far, but installed a Facet Posi-flow on the inboard side of the firewall, downstream from the selector valve. Have not used it inflight yet - through the entire power on/power off stall testing - both full and low tanks. Have had low pressure warnings from the dynon on extremely hi aoa/power regimes, but not one stumble in the Jabiru 3300 Gen 4. Have not had to use the pump, but like it there "just in case."
Jim Nichols and I have similar builds with the same fuel pump. I only have 15 hours in phase 1 so far, but have not needed the pump in flight. The only time I use it is before starting when I first turn the valve from fuel off to both tanks. Like Jim, I like having it there "just in case".