Weed Eater Primer bulb won't release?

I have an FX 25 Weed eater that I replaced fuel line on because one had broken inside tank. After replacement of lines wouldn't start, runs when I put stater fluid in plug hole as long as fuel lasts then dies ,
I then completely tore down carb & rebuilt it with Walbro kit & replaced primer bulb new fuel filter everything fuel related but still will not start , primer bulb when pushed will not release, swapped fuel lines thought maybe wrong but bubbles in tank. took apart several times to make sure something is not installed wrong by Walbro Illustration everything looks fine. Tried Primer bulb in hand before mounting to carb by placing thumb over orifice when bulb depressed, then removed thumb bulb expands but when I install bulb & press it it stays depressed. Why is something so simple so hard to get working. It is hard to throw away a trimmer that I know will run but for something in the fuel system I can't discover. Any Hints are gratefully appreciated.