Hi, In Nop Store Locator 4.2 version, i can see Map Zoom level is not working. I tried with entering maximum and minimum zoom levels. But it's not working. In 4.1 it's working fine.
In this case, I would advise you to enable Manually Set Map Bounds (initial map position) option enabled and set Latitude and Longitude. Then the Map Zoom Level should work as expected.
Let me know if the issue persists.