[SEL] DELCO LIGHT PLANT HELP NEEDED

[cgandree at mchsi.com]

Looking for some words of wisdom on my Delco Light Plant.  Trying to start the engine but seems like I am not getting gas to the carb.  On my model the gas tank is below the carb so after taking the fuel lines off to check for blockage of which there was none discovered that there was no check valve.  I cleaned out the old gas and thoughrly checked for some sort of check valve that might of fallen off into the tank but none to be found.  Last time I ran the plant was about a year ago and it started and ran soomthly. My question is were they supposed to have had a check valve or is gas sucked out of the tank by some sort of vacuum when the engine runs?  Any help would greatly be appreciated.
Thank you in advance.
Curt Andree