I remember my brother soldering his NSU moped petrol tank. The fuel tap boss solder joint had cracked.
All was going well, then BOFFF and he now had an instant added pint or two capacity. At least the filler cap was NOT fitted so no real harm done.
Had a little more luck today. I found the kill switch circuit shorted to ground.
There was this instant, if short lived, growl of 42ci boxer power, with several tablespoons of rust blown out of the exhaust for fun. Next up is the carb and the wiring.