No vapor seprator in the trunk.
This is what I had read that got me thinking about this path.
By Slantsixdan.
m you're asking about is present on '70 California cars and '71 50-state-plus-Canada cars. '71 was the first year all cars in North America (not just California cars) were equipped with evaporative emission control systems (ECS). This first-two-years system is more complex than the relatively simple '72-up system.
The '70-'71 setup uses a complicated fuel tank: there is a small inner tank at the top of the main tank and connected to the main tank chamber by a very small passageway, so that the main tank chamber fills up with the secondary chamber still mostly empty. The gas pump nozzle detects a full tank and clicks off, you hang up the nozzle and drive off. Over the next little while, the secondary tank fills up from the main chamber, dropping the fuel level in the main chamber so as to prevent fuel leaving the tank when things warm up and expand.
These '70-'71 ECS fuel tanks have four vent fittings, one at each corner of the top of the tank. These are brought together in the trunk to a more-or-less vertical vent cylinder leaning against the left wheelhouse — that's what you're seeing. This vent cylinder has five hose fittings: one for the hose from each corner of the tank, and one for a hose connecting to a line that runs up to the right rear corner of the engine bay. it is not supposed to vent into the trunk!
Inside that vent cylinder, each of the four fittings from the corners of the tank continues vertically, each to a different height. The fitting to the engine bay continues inside the cylinder almost to the top. The idea with the 4-corner venting and the different-height pipes inside the cylinder is that no matter what angle the car is at, in what direction, there will always be at least one vent fitting above the liquid-fuel level, so there'll always be a vapour vent, thus preventing pressure buildup that would force fuel vapours out into the atmosphere.
The '70-'71 ECS is also unique and interesting in that it uses the engine crankcase to store fuel vapours piped forward from that vent cylinder in the trunk and from the carb bowl. The interface point is a fitting on the fuel pump body on slant-6 cars, or extra fittings on the engine breather cap on V8s. When the engine is started, the collected vapours are drawn off out of the crankcase via the PCV valve. This system does a reasonably effective job of containing the vapours, since the crankcase is well sealed, but it can cause hot start/hot idle problems, since there is no control over when the vapours are extracted from the crankcase. Most of the unburned hydrocarbons wound up out in the atmosphere anyhow, having been first put through the engine (and emitted as black smoke).
