Zombie.Humanoid.Health not changing from 100, please help?

Hey guys. I have been having a problem with zombies, I can't change their health from 100, I have tried through script (didn't work) although the exact same script worked for maxhealth (so there were 100% no scripting errors) I then tried by editing the zombie's humanoid stat which even though visually worked as soon as I got into the game it reverted back to 100, I then manually edited it in play solo and the game crashed. Zzzz. I had a minor breakthrough by going zomb.Zombie.Health = zomb.Zombie.Health +300 (Zombie is the name of the humanoid, assume zomb is the zombie) I have no idea why this worked but it did but ONLY IN PLAY SOLO! I then tried adding my first attempt (script form) into a local script and testing it at my live place but that didn't work either.

So scripting helpers, can you help me change my zombie health away from 100?