CIS Flowtech did not really answered my question whether my FD needs such a spring...

Any idea what can cause such suction in the fuel lines, holding my plunger up ?
Between my WUR and top of FD there is also a diagphragm damper.


Could this be a possible root cause ?
I checked the damper and I can blow air easily through it, so it is not blocked.
Any idea what the small screw is used for on this damper ?

kr
Gerrit