I have never lost prime on my MX machines, the BX2670 is another story. I had to bleed the injector lines more than once.

If you did not turn the valve off or if the valve leaked you will have to purge the air from the fuel system. The best way would be to follow the fuel line to the next fitting and try purging air from there and so on until the air is purged. My BX 2670 was a real pain losing prime when I replace filters.