started having longer cranking times last week till finally truck didn't start after refueling. pushing the primer bulb didn't help.it never got hard. used ether to get started ( was 200+ miles from home) and got going. truck runs fine once started. Ordered new filter head since the one i had was rebuilt 2 times. replaced head and still couldn't get system primed. uses shop vac to push fuel from tank to filter, truck started and i test drove for 20 mins.no issues. cutoff truck and restart but cranking still longer than normal and truck starts. let sit over night and no prime and will not start. pushing primer bulb i'm constantly getting air from bleeder. i do not see any fuel leaks anywhere but i know it's sucking air. i have a kennedy pump so i figure once it gets started the pump is keeping a constant fuel flow, but stlll no visible signs of fuel leaks. i tested the primer bulb before installing on truck by placing finger over intake tube and it had good suction. Is there a way to test for where air is entering the lines?