I think using a return line, using the port plugged with the brass fitting in your pic, is a good idea for a few reasons -- reduces the smell of gas fumes, saves fuel by keeping it from evaporating into the atmosphere. It can even smooth out the idle in some cases. But most here don't use it for simplicity's sake. It's up to you.

http://bbs.zuwharrie.com/content/top...9de8#msg761158