Replace your leaky old fuel valves
with freshly made ones. This Italian made flip over type is correct for Falcones, Airones, and lots of other Italian bikes. The threads that go into the tank are the very popular 10X1mm and the fuel line side is 1/4" BSP threads.
NOTE: Some older MV and Guzzi singles use the long obsolete 9.5x1.0mm petcock thread size. These 10mm petcocks will not fit unless the gas tank threads are tapped out to 10x1.0mm. Please check your petcock threads before ordering.