how does the sirion fuel system work ??


hi everyone
we still have the year 2000 m100 sirion; it has been great
how does the fuel system work Unknw the manual shows a 'carbon cannister' and says to check flows in/out.
my economy started at about 19.5 kilometres per litre but now has dropped to about 17 kilometres per litre; so i put some injector cleaner thru . . . no real difference: so i went looking for a filter

anyway, i have never had a petrol injected engine before [only diesels]
thought i would ask how it worked