When fuel gets added to the tank, the EVAP system allows the fumes to escape the gas tank through the canister and the vent valve.
If the vapor canister is clogged or the vent valve is shut, it will not allow fumes from inside the gas tank exit as you fill up. This will create a bottle neck effect. Which will lead to a very slow fill up or overflowing out of the fuel filler neck.
I have attached diagrams of the canister and the valve below for your reference.
Please let me know if you have any questions.
Images (Click to enlarge)
Thursday, February 24th, 2022 AT 6:18 PM