fuel trap function and replacement

[RedTriumphTr6@aol.com]

Guys, my late 74 has more emission control garbage on it than those of you 
fortunate to own cars made in other years.  One thing I did notice about the 
74-76  cars that they do have in common is fuel traps, although mine seems to 
have more of them (3).  What is their function, and how do you know if you 
need to replace them?                                             Bob Pierson