The gas tank will vacuum lock with no vent and starve the engine for fuel.
The vent is the charcoal canister. That is a good thing to have working because it also ties with the PCV line. The PCV controls engine sludge and won't operate right without the added air flow from the canister.
The return line is there to prevent vapor lock on a hot shutdown.
86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com
(10 new albums added Sept 16/10)