when you installed the electric fuel pump did you stick with rigid line or "flexible carburetor fuel line" (it is possible to create enough vacuum to collapse the flexible line if venting is inadequate) "fuel injection flexible line" is very rugged (& a little difficult to work with) & will not collapse. i ran a single vent line alongside the filler to a brass plumbing fitting & it is only visible when "fuel door" on bed is open.