1980 720 bobcat. wisconsin vh4d. i had to put a fuel filter inline before the pump. prob now is after it sits for 20mins or so the fuel drains back to the tank. am i missing a check valve somewhere? any ideas? from the tank theres the fuel line to a clear filter then runs to pump. i had to install a primer bulb to aid in starting. should the fuel pump not selfprime when i turn it over?