MG Car Repair: Rubber vapor hoses in the trunk, oil pressure switch, charcoal canister

Question
Hi Howard,
I have a 1977 MGB. I noticed the other day that there were 3 pieces of rubber hose in the trunk on the right hand side that had rotted out on the ends. I also noticed that there was a vent nozzle coming from the floor of the trunk next to where the filler hose goes into the gas tank. The other pieces were on the far right of the trunk underneath a round device mounted to the trunk wall. It also had 2 vent nozzles on it. I believe it has something to do with capturing vapors from the gas tank. The question is....it appears that one hose would go from the nozzle on the trunk floor to one of the nozzles on the round unit on the wall. It also appears that another hose would come off of the second nozzle on the round unit but it doesn't appear there is anything for that hose to connect with. Can you help with where that hose connects to?
The car is difficult to start, does diesel when the ignition is switched off and the trunk has an odor of gasoline.
Thanks

Answer
Hi Ed,
One hose comes from the top of the fuel tank which is the tank vent pipe and it goes to the round can (vapor separator)and from the separator it goes all the way by a steel line under the car to the charcoal canister under the hood.

If your car runs on after you turn it off then the anti dieseling valve system is not working which is attached to the charcoal canister also and also has a vacuum hose from the manifold to apply manifold vacuum to the vent line from the carburetor float chamber. When you turn the key off the valve allows vacuum to be applied to the float chamber vent line which transmits vacuum to the fuel in the float chamber thus preventing any fuel from exiting the main jet. Thus preventing run on. The valve it powered all the time and grounded by an oil pressure switch. When the engine is shut down the oil pressure goes down and thus the oil pressure switch quits grounding the valve. The valve then allows manifold vacuum to enter the float chamber and prevents any more fuel from leaving the jet.
To test the valve just remove the grounding wire off of the oil pressure switch and scratch it across a good ground and listen for the valve to "click".

Howard