I looked at my neighbors' 1972 220 today.
The black plastic tube at the front of his engine connects with a 2 inch rubber hose to a matching black tube that runs from under the battery tray, parallel to the metal fuel lines, along the frame rail next to the steering box. It parallels the metal fuel lines under the drivers floor to just inboard of the rocker panel then turns inward under the left rear seat-floor to connect to a plastic valve assy (I think it's part of the vapor recovery-emmissions system) near the front muffler/ exhaust system. This valve has another plastic tube coming from it that connects over the front of the gas tank.
If you can't find any of what I've described, the plumbing may be different on your 1974 model. Good luck.
Happy Motoring, Mark