I have a 91 Electra Glide and if it sets for a while all the oil drains from the tank into the motor what can I do to stop that? Thanks

 

Oil is leaking past the check valve in the oil pump. It's either dirty or worn out You should remove the oil pump. Clean it out and replace the check valve ball (looks like a ball bearing). The service manual for '91s shows how. The ball can be replaced with pump on the bike and its chamber cleaned. But if there's any tiny debris in the pump it will only leak again. It's old. It probably needs it.

 

Great advice--and maybe look at a new pump, since you're there.