I thought that by '67 they had stopped using vented caps, and used used ones that seal tight like my '78. But on my '78 I have an EVAP canister with a line to the tank, so expanding gasses have somewhere to go. I'm reading up on the '67 to '70 Camaros, and it seams that the cap is a one way vent allowing air to come in, but not for vapors to escape. And there was a return line attached to the fuel filter I think to control carb vapors? Prior to the sealed tanks, they were just open venting which contributed fuel vapors to smog.
Yeah, your Holley has two upward vents sticking up from the bowls. There's no easy way to hook them up to an EVAP canister. But I suppose you could use a V8 one that is missing the carb valve on it, and just hook it up to the timed port. You would need the thermal valve for the water neck that is for the EGR/EVAP, and another port on the neck to screw it into. That would provide the vacuum to the canister valve. Then you need a line back to the fuel tank. But I don't know if there is a vent pipe to hook up to on the pre-EVAP tanks?
