Teen Beach Movie
I was barely able to get a side view of the tank, but this later image of the bike makes me think it's a BSA of some kind: You'd think in a movie with bikers, they'd have more bikes. There's another shot of the apparently '70s Volkswagen Beetle in the background of the thumbnail. Yes, definitely BSA, probably a Lightning.It is either 1968, '69 or 1970. Finally! Now see if you can identify this one to the right of Grace Phipps: Link to "a.dolimg.com"
It only took one day