If your primer button does not feel it is getting harder to push down and you do not hear a "buzzing sound" after you push for a while (coming from the overflow valve on the back of the IP) then you have an air lock on the top of the secondary fuel filter. Just loosen the large bolt (22 mm) that is in the middle of the metal fuel filter to the left of the primer button. When you start priming again you will get all kinds of bubbles and fuel. When you only get fuel tighten the bolt back down. That is an aluminum housing so don't overtighten. A small bubble in the prefilter is ok. Depending on whether you tried to start the car while it was airlocked you may or may not have to crack the injector lines to help get the air out of those as well.

__________________
Marc-André

W115 1975 300D "Geraldine"
W115 1976 300D parts/tutorial car