Plunger im Verteiler hoch gezogen nach 3 Stunden

Hi,

this is a 1 stage pressure regulator with an addtl. closing valve towards WUR that avoids flowing off of fuel from WUR after engine stop. It does not open if a vacuum starts to build on top of plunger and pulls it upwards.

Today I did some further testing :
1. cold start is only difficult when I directly try to start the car (plunger is in upper position) . Solution, turn the key on/off within a sec so that pump doesn't fully prime and plunger gets back to its rest (lower) position
2. warm start after 2h is also difficult. Cranking 5 seconds before it starts

Then I had the idea to pinch the return line of the distributor after car had run so that no fuel could flow back to the tank during 2 hours.
After 2 hours I tried to start the car and it immediately started.
So this means that my fuel distributor and/or WUR is not holding the fuel for a longer period after shutting down
engine.
This could explain why fuel returning is indeed sucking on the plunger in my FD and creates a kind of vacuum.