[H. L. Chauvin]

FWIW:

1. If your tank is rusty and/or dirty, or if you fill up with dirty gasoline; &,

2. If your tank has fine particles of iron rust and/or sand from any source; then

3. Iron & sand are harder than the brass shut off valve & they will eventually scratch the brass tapered device & will eventually cause the shut off valve to leak ....... some have an in-tank fuel tank filter which can greatly help to prevent shut-off valve failure.

4. Sometimes some deleterious fines get passed the "original" Model A fuel filters & can prevent a float valve from sealing off the gas flow -- hence, a carburetor leak occurs.

5. A Model A gravity fed fuel tanks sitting up high are similar to a vehicle with a lower fuel tank below the carburetor ....... but with the fuel pump running constantly.

6. Leaks or no leaks, with a High-boy air filter, it will always remain free of liquid gas.

7. Lots of good helpful information in above replies -- each to his own -- sometimes Model A fires can be prevented.