AVS Bowl Vent Valve Fitting....cap it?

[kawahonda]

I've always had a cap on my bowl vent valve. My engine builder said that's not correct and that needs to allow venting.

Where would such a thing run to? Anyone have pictures that tell the story? I notice on the bottom of my air cleaner that there are two "screw holes", but nothing there. Perhaps it was some sort of canister that's mounted under air cleaner?

[Chryco Psycho]

typically the bowl vent was sealed with the fuel system so no gas fumes are released to the atmosphere , nevermind all of the fumes released from the fuel tank as it is filled everytime 
So it was connected back to the tank in early years & into a carbon canister in later years , the AVS still vents inside the aircleaner out of the top of the carb so the connection can be plugged .

[Bullitt-]

a quick google found this discussion, most state the vent has it's purpose so plugging it may create issues.  If you have a service manual for your model it should reveal where the vent connects. 
https://board.moparts.org/ubbthreads/ubbthreads.php/topics/510022/why-do-some-avs-carbs-have-a-bowl-vent-valve.html

this statement seems to be the most informative if correct
" The valve closes at any throttle position other than idle. The bowls are vented primarily through the air horn to insure pressures above the fuel in the bowls equals the pressure above the venturies, regardless of any potential air flow restrictions (i.e. dirty air filters). The idle bowl vent intended purpose is to release evaporating fuel vapors outside the air cleaner under hot idle & heat soak engine off conditions. Without the idle vent valve, fuel vapor collects in the air filter housing making for hard hot starts and unstable over rich hot idle.
As stated, for E.C.S. the idle bowl vent valve was enclosed and fitted with a hose nipple to collect and later reuse these vapors."

[kawahonda]

Hmm. Mine is ECS.