I had one 5 years ago that still makes me cringe! To prime, they have to build pressure in the bowl. So that means the bowl, rim and bowl seal must fit well and be corrosion free. New and new helps. Also, the air filter screws in the end have to be in place in at least some series.

All that stuff was replaced. The sticker says "Push to Prime". Notice that there is no limit on the number of pushes? :)