What is the purpose of the two vent tubes that stick straight up on the Motorcraft 2150 and 4180 carburetor air horn that vent the fuel bowl into the air cleaner? Should these vents be closed if the vehicle is equipped with the evaporative emissions?

If they remain open, what is the point of having the two LARGE external tubes that vent the fuel bowls to the charcoal canister?

 

Federal mandates rarely make sense.
Those who make the mandates,make even less.

 

The vent tubes into the air cleaner are to equalize the fuel bowl pressure with the carburetor inlet air pressure.

The vent tubes to the evaporative emissions system are blocked by solenoid valves that close when the engine is running: their purpose is to allow fuel vapors to vent to the canister when the engine is hot and shut off, rather than building pressure.

The former are necessary for proper operation when the engine is running; the latter are for emissions control when the vehicle is parked.

 

Thank you for that very clear and concise answer, bkaul. I think I understand it now.