Ginge,
The amal valve will drop your maximum available boost pressure. If your not using boost pressure then theres nothing to gain this way.

Your car ran with reasonable fuel efficiency when i tested it so make sure your not doing anything really daft with her like:

A) Brakes binding. (VERY common)

B) Leaving her to warm up for 10mins stationary.(what a fookin waste of juice if you only live 5mins away..roflol)

C) Have a sensor problem. (Unlucky to have one so soon after you were here)

Just a few thoughts pal.