Once fuel system is primed, unit fires right up but only runs for a brief period before shutting down from no fuel. Once the fuel system is primed and air removed, unit will start without issues but only for a short time before shutting down again.
I think it’s either sucking in air through a leak, or the fuel filters are clogged up.
Please start by changing the fuel filter. If it’s clogged it could be that priming the system gives enough pressure for enough fuel to go through to allow the engine to run for a short time.
If it’s a leak, air can get sucked into the fuel system. But this is also made worse if the fuel filter is dirty, as you’re creating a vacuum after the filter as the fuel pump tries to draw fuel through it.
Hope this helps 🙂 Let me know if you need anything more.