Missing Vapor Recovery System

My 73 is missing evap canister and all elements of air injection system. All I have is a roll-over vent valve. Utility of which I question since the fuel cap seems to not be at all sealed. I have historically simply ran fuel to my carb. There were two brittle tubes running to the vent check valve.

Am I correct in thinking the roll-over valve prevents free flow of gas from tank vent straight to the evap canister, dumping fuel into a flipped engine bay? And since I dont have an evap canister is there any reason to keep the roll-over check valve? Seems like I'm presently lawn-mower simple. I'm not opposed to evap system but without a canister/filter the rest seems superfluous. Thoughts?

Also, I'm exempt from emission checks, and dont run enough miles to hurt the earth

 

Yes, it's not called a roll-over valve in that era, but instead a liquid check valve. It's just a needle valve on a float, and keeps liquid gas out of the vapor system. Those two tubes are intended to always vent the highest corner of the tank into the check valve.

Are you using the factory air cleaner? I have no book for '73, but I recall it followss the design that uses Bernoulli effect to draw vapors from the charcoal bed. There are only two hoses, the hose from the check valve to the vapor canistr, and the hose from the canister to the tap in the end of the snorkel of the air cleaner. When the engine is running, intake air through the snorkel makes a mild vacuum on the tap in the snorkel, and draws clean air in the bottom of the canister and across the charcoal bed. There is picks up vapors that have been passively trapped by venting the tank through the charcoal. The charcoal has an affinity for the vapors, but enough clean air flowing across it will vent the vapors into the air low (it's all about the concentration gradient).

Without the canister, the check valve is pointless. Without a sealing cap, the whole system is pointless. You may as well remove the valve and run the vent up as high as you can and vent though a fuel filter. That makes a good baffle for the vent end. Or you could put the canister back and get a well-sealing cap.

 

A charcoal canister from a salvage yard is pretty cheep. You can source one from a mid nineties Chevy that only has two ports one from the roll over valve to the canister and one from the canister to the air cleaner as Tim mentioned or depending on your carburetor a ported vacuum fitting. Ported vacuum only occurs at partial throttle to clean the charcoal canister from the fumes. I’d certainly retain the roll over valve for safety reasons and venting the tank to a canister keeps your garage from smelling like gas.