I found my tank breather wasn't working and traced the problem to the two jets that's screw into the bottom of the tank both being total blocked with corroded aluminium. Removed and cleaned out easy enough. As a part of the same exercise I decided to strip and clean the inside of the fuel cap. Like a dick I didn't take any pictures and now I'm not sure if I've put this valve in the right way round. Can anyone confirm?
It looks like you have it the correct way around. You can see pictures and explanation of the fuel cap parts in the second post on this thread http://www.ukmonster.co.uk/monster/showthread.php?t=50885