Where can I find the serial number on a 1985 250 Honda four wheeler?

Answer 1

Front frame cross member (flat piece of metel).
http://www.bikebandit.com/partsbandit/OEM-Parts.asp
Look at the frame. At the very front is a round tube that is attached to the left and right frame.
Just above and to the rear of that, is a flat piece of metal that is attached to the left and right frame.
If you have a hard time reading it with a flashlight, put a piece of paper over the #s and rub the paper with a pencil.

Answer 2

should be on the front forks or frame rails - etched into the metal