are you referring to these?
http://www.midwest-bayless.com/fullView.asp?sf=y&nb=1&id=%27251937197%27&img=http://images.marketplaceadvisor.channeladvisor.com/hi/67/67274/4388570-OE.jpgFactory OE metal-bodied one-way fuel check valve for use in the fuel supply lines on most carbureted Fiat cars with mechanical fuel pumps. Fitted near the fuel tank to prevent siphoning of fuel back to the tank.
If your car requires a lot of cranking after sitting overnight to start, this could be the culprit.
This is the early "ufo" (flying saucer style) as original production fitment by Fiat.
OE style metal unit is very difficult to source.
Fully interchangeable with later style round body units.
Fiat USA superceded from metal ufo style to the unfortunate plastic-body round replacement which is prone to rapid demise.
http://www.midwest-bayless.com/storefrontprofiles/DeluxeSFItemDetail.aspx?sid=1&sfid=208227&c=193435&i=255092515Factory OE metal-bodied one-way fuel check valve used for the evaporative emissions venting system on most carbureted Fiat and Lancia cars.
This is the later round style as original production fitment by Fiat.
OE style metal unit is very difficult to source.
Fully interchangeable with earlier style "ufo" (flying saucer) units.
Fiat USA superceded from metal to the unfortunate plastic-body replacement which is prone to rapid demise.