How does the primer bulb on a string trimmer pump gas?

I have a Stihl FS55 string trimmer. Engine would start but wouldn't keep running so I disassembled and cleaned the carburetor using carburetor cleaner in a rattle can. Reassembled and installed and found the primer bulb won't fill with gas. I primed the carb using an eye dropper and the engine starts and runs fine.



Disassembled carb again. Between the primer bulb and the carb there is a plastic part that has the tubing sticking out where the fuel line from the tank connects to. The primer bulb is supposed to suck gas from the tank through that tubing. When I try to blow or suck on the tubing it seems blocked. I assume that I should be able to blow air into the tubing (like gas going into the primer bulb) but not be able to suck air out of the tubing. Is that right?



Thanks,

Yardguy