[Chaplin]

Kristen-
Cowtown may be right, but here is something else to consider along the same lines. I don't think early ERAs had a screw on gas cap below the monza cap- (new ones do). If I'm correct, on yours you just simply pop the cap and there is your filler neck. If the rubber seal around the monza cap has deteriorated from age, you may be getting fumes coming right up from the tank. I think some people have stuck racquet balls or tennis balls in the end of their filler necks to "seal off" the tank, and then closed the monza cap with the ball underneath.