That is a good idea actually. If you look at scale pics of the Fokker DR1, there were tubes exiting each side of the fuselage behind the firewall. These were the air intakes for the carb. I have used these before as guide rods to the needles on my carb. My engine will be boxed back from the firewall and may have half the carb in and half out. Not exactly sure yet where it will land exactly. A tube running to the carb for priming might be the easiest solution though.