It needs to vent freely when not running and be closed when running. From what I have read, if you can't find a replacement, it is just best to plug the vent to the charcoal canister. The carburetor will continue to vent inside the air cleaner; it just won't be captured by the charcoal canister.
'83 Scrambler (CJ-8) / 258 / T-5 / D-300 / DANA 30-AMC20 (3.31)
'88 Grand Wagoneer (SJ) / 360 / TF727 / NP229 / DANA 44 (2.73)
'05 Wrangler Unlimited (LJ) / 4.0L / NSG 370 / NV231 / DANA 30-44 (3.73)
'15 Wrangler Unlimited (JKU) / 3.6L / 42 RLE / NV 241 / DANA 30-44 (3.73)