I have learned that our carbs. wear out the bushings on the throttle plate shaft, (mine has not done it...). Check the plug, (round, about the size of a button) on the back of the carb. facing the rear of the car. I had to put some gas proof sealer around it to stop the leak. The shut-off valves rarely wear out. Find a used one if that is the problem. You could also check the needle valve for the float. If you replace it, use a Solex with the #72 on it. Make sure the copper tube that goes into the top of the carb is pushed all-the-way-in. Any other questions, post, and I'll reply with other work I've done on my carb.
Hope some of this helps. Llet me know, Patrick.
'72 Super. Paint-7/20/09, 400+k miles, New engine case "41" Brazil, rebuilt German heads, new Bosch electrics, new Solex German carb. new German silencer. Built by Steve Tims Performance/Enterprises, Riverside CA. '73 OEM airfilter, (Fram elemement), chrome stock wheels, daily driver, 25.46-27.50mpg, driven 20+years.