My recently-purchased 1975 164 was developing a lot of pressure in the fuel tank. Yesterday, after filling the tank and driving several miles, I noticed a black tube hanging behind the rear axle on the left hand side of the car, dripping gasoline. I've since worked out that this tube is meant to be attached to a line that carries fuel fumes to the carbon canister under the hood. The overpressure in the tank seems to have eventually caused the tubing to come free. There is no longer any pressure building up in the tank.

I've looked at various parts break-down diagrams and have worked out how the pressure due to fuel expansion and vapor pressure is meant to be relieved through a "valve" at the top of the tank and through the tubing to the carbon canister. My system has another "vacuum valve" at the top of the canister. Since pressure was building up in the system, clearly some part of this system is not functioning correctly. It could be a block in the lines. But it seems it could also be one of the two valves or the canister itself.

I am unclear, however, what the purpose or function of the two valves is. If I were to remove them, is there some way that I can confirm that they are functioning properly? Can someone advise as to what the proper function of these two valves is and how they can be tested?

Also, is it normal for liquid fuel to make its way into the tubing? Is this an indication of a problem with the system?