I have read about machines having to be started by hand, but don't remember if there was some trick to get it going on its own. It has been years ago, but I know April & Carmon (now singer-featherweight.com) were quite helpful when I called and asked about a pinker.
I like Joe's suggestion.
I'm wondering if there is some thread or even hair that is caught somewhere, making it harder to turn at a particular point. I had a FW that had a more pronounced hard spot that I tell about
FW-HASB ?? fixable? by me? - very long winded I finally fixed it. I don't remember exactly but it had something to do with the rotary hook shaft. There is a flat spot on the rod that the set screw needs to be on. I thought the screws needed to be in a straight line, but the service manual (
https://cdn.shopify.com/s/files/1/09...13128764594508 pg 11 ) doesn't show that they are. Unfortunately, the link doesn't work of the video that I watched and the one they have now doesn't seem to be the same.
Good luck on getting your FW working to your satisfaction. They are fun machines.