Having used a few different Lil Phil guns over the past few decades this story is what I'll taken as standard performance. I also attribute it to air in the top of the cartridge where the pump's inlet is. If the pocket is small you can pump the air away and regain grease flow with enough handle strokes, many strokes. I'll pull out and reinstall the cartridge sometimes and if that still pumps air I'll install a new cartridge, the old one gets scraped out and into the bench top container. It is the one aspect of these guns that I wish was different. Andy