|June 9, 2010 - Mystery solved!|
The "swirl tank" is actually a vapor separator as part of the emissions control system. What I thought was a return line was actually a vent for the fuel tank. The vapors collected in the separator traveled up to the engine bay into a charcoal canister and were eaten by the engine. Having the separator in place kept raw fuel from getting fed to the charcoal canister when a full fuel tank would expand from heat.
I can hijak the system to work as my return line - but then there's no venting capability for the tank. Older MGBs had a vented gas cap that let the pressure in the tank stay constant regardless of temperature fluctuations or fuel use. The downside is that they can drool fuel with a full tank on a hot day.
Luckily, the green MG parts car that lives outside is a 1969, and comes with the vented cap (on the right) and appropriate fuel filler tube. Since the charcoal canister from the 1972 car was damaged when I got it, that's my best solution. Looks like I might need to get a new cap though.
tags: packaging, suspension, fuel tank