gas gauge not working

hi i am a newbie to this site and am having a bit of trouble finding an answer to question, my gas gauge dose not work every time i start my car it dose a counter clock wise spine and stops near the bottom un till i start up the car. the car buy the way is a 67 camaro i thinking it may be the sending unit but i thought i would ask first to see if any ones has had this problem thanks for any advise

Could be the ground, but generally, when a Chevy has a bad ground on the sender, the guage goes clockwise, way above full..........But, stranger things have happened.