[slob]

The fuel system should self-purge/prime.
As gaza says kinked pipes are quite likely.
The pipes would have to be the right way round, as the pressure regulator sits at the return end of the rail, venting excess pressure back to the tank. If labelled: M is feed (mandata) & R return. I would expect the QR fittings to spray fuel everywhere if not properly connected, a quick wipe with grease or a squirt of chain-lube often helps ease the o-rings into place. A blocked fuel filter would also cause problems, as this is a bit of a faff to change and may be overlooked during servicing by the uneducated or lazy but should cause poor running rather than a no-start situation. If the bike turns over ok but doesn’t fire, try a new set of plugs as the 796 seems quite sensitive in this area, even if the spark looks ok when not under compression.