Evaporative Emissons System Gas Cap

[fiddler]

The Gas Cap on my 1974 Chevy Step side has a cracked and worn out gasket.  I am going to replace it as it is venting fuel outside when the truck is just setting.  Price of gas and pollution standards makes this prohibitive.  I am faced with the choice of a vented or non vented cap depending on whether or not the truck has an evaporative emissions system.  Can anybody out there tell me if that was standard on the 74 or how to check for it?  (Maybe look for a specific piece of equipment or something?  Thanks in advance for your help.

[Captkaos]

A 1974 truck won't have a vented cap.

[zieg85]

The only way to tell for sure is if you are lucky enough to have the original sticker on your core support/air cleaner.  I have my Chilton's book covering GM's Full-Size Trucks 1980-87 repair manual that shows copies of the different stickers for the vacuum hose routing depending on the emission package that came with the truck.  You may find the same book covering 1973-79... My $.02

[Captkaos]

The GM manuals for the 1974 is here:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,25639.0.html