How tight should the spring be on the steering servo on my Warhead? I have taken the bottom skid plate off and it is at the bottom of the threads?

you should tighten enough so that there is just enough play that when you turn the wheels by hand that is will open the servo saver slightly, try it like that, see if its tight enough, if not give it another turn, but always make sure that the servo saver opens, if it doesn't your to tight.