What happened to gasoline in the mid 1970s?

Wouldnt gasoline flash off hydrocarbons through evaporation?
Yes depending on the temperature and pressure some components may or will.
See the distillation curves in this post.
post #100 Too much timing?

I'll edit this based on RRR's post below.
If you mean change from hydrocarbons to something else, no. Its just a vaporized hydrocarbon. Similar to evaporated water is still water, just in a different state.