Quite a while ago I made a map for 2v2 (I sometimes play with three other people I know on the weekends) but the map has had a problem with the spawn points. The play area was rectangular shaped and very short, and it was made on foundry. At the begining of any slayer game (I've never tried any other gametype on it) players spawn on the raised areas with stairs leading up to them, near the back hallway, even though I made the map on a canvas, which had no spawn points there. HALP!
You have to set the starting gametype spawns. To do this you have to go into Monitor mode, press Start and select a gametype, most likely slayer. Then it will start a new round and you should be able to delete these staring spawns and then add them somewhere else. Objective games are ahrder and I won't get into that because you only asked for Slayer. If you need any more help, you can add me on Xbox Live. GT is HomerSPC