As Chryss said, setting default zoom level doesn't yet seem to be possible in the Lite version of Google Maps Engine.
It is, however, possible with a free account at full Maps Engine (Google Maps for Business), but that's a whole other animal to work with and takes a bit getting used to.
If you don't want to dive into that quite yet…
New Google Maps still lets you "Return to Classic Maps", so if you want to go that direction with a simple map, you don't need to export, open etc. Just switch back temporarily, create your map there, and get the "classic" embed code, with zoom levels and everything.
However, I didn't much like the solution of going back to the old maps, so I chose another inelegant workaround:
- Add another layer to your map.
- Add some points of interest in a radius that roughly corresponds to the zoom level you want. (E.g. for the B&B site I was making, I added a layer of Major Airports)
- Uncheck the new layer, to make it invisible.
- Embed the map.
The embedded map should then be zoomed out to get all locations in the map, even if the layer they're on is turned off by default.
Of course, the user can simply check the box to show the hidden layer, but if you make that layer useful or relevant, that doesn't have to be a big problem.