Had one for my son long time ago and was great fun dependable sled. The vent in question I’m sure is only a vent tube that used to go in front of the chain cast and vent through the belly pan. Some vented back to right and vented down inside the cowling by your right foot. Any size fuel in that you can get over the end will work and if your line is a little big just clamp it. You can run without it but it’s messy and smelly.