The carb faces rearwards and there is probably less than 3/4" clearance from the firewall. The way the ARF is setup there is an 800ml fuel tank the end of which protrudes through a 1" diameter hole. So the plumbing tubes are going to be very close (and maybe a bit above) the carb opening.

And, yes, it's have a vent line to the exhaust. I've never had a model without a vent line and don't really understand how that would work.

The idea of an additional line on the fuel line sounds worth pursuing. My usual method is very primitive. I've always just have three lines: 1) fuel to carb 2) tube to exhaust and 3) a third "fill" tube that dangles more or less free.