I have a TB70SS trimmer. I used my trimmer on half my yard with no problem, turned it off to cut the grass with the lawnmower, then tried to turn on my weedeater again, and noticed the primer bulb would not fill. I thought it was the bulb, so I went and bought one and replaced it. It still does not fill so my trimmer will not start. Checked and replaced all fuel lines. Why would it stop working suddenly?

First, the primer/purge bulb does NOT have to fill completely to function. It's purpose is to remove old fue and AIR from the fuel system (carb) and move it back into the fuel tank. You normally will have an air pocket in the bulb. An air leak in the fuel system or loose carburetor screws or fuel lines in the wrong location can cause your problem. Check the fuel line and fuel filter for a good connection in the fuel tank. Remove the fuel pump cover on the carb and make sure the very small, round, wire mesh filter is not clogged with debris. When old fuel lines deteriorate, they crumble and if the filter is broken off, the fuel line to the carb will ingest bits and pieces of old fuel line. Check all these things and post back.Sometimes, if the bulb is on the carb, a check valve in the carb can stick. When you check the condition of the mesh filter inside the carb (opposite the side with the vent hole), then liberally spray with WD 40. Strong solvents and cleaners can SWELL up the tiny check valves in the carb, causing problems. So you see, it is hard to pinpoint exactly what happened without some removal of parts and diagnosis.