Greetings:
Fuel flow is gravity-dependent. Because the carb has to be open to the air - to mix with the fuel when the engine is running, think of the carb as an open pipe dangling below the tank. It is a drain.
Because liquid wants to flow down a drain Mr. Honda designed in two obstructions to this flow when you turn off your engine:
1. The fuel petcock. When the engine stops, it stops supplying vacuum to the diaphragm within the valve assembly. WHEN IT'S WORKING CORRECTLY, a little valve is supposed to shut off and plug the drain in the line that leads to the carb bowl. Yours is not doing this. If the fuel line is cracked - rubber gets brittle and vibrations are constant - this alone could explain your leak. If the fuel line is intact, the next feature prevents the fuel from leaking out the carb:
2. The float needle. When THAT is working correctly as the bowl of the carb fills, ithe float rises on top of the fuel and applies pressure to a little rubber-tipped cone that plugs the hole leading from #1, preventing the bowl from filling above the desired level. If it does not, the fuel keeps right on filling the bowl until it climbs up the jet tubes and out the carb throat.
Both of these features can be defeated by spooge from the tank. Rust, resin gums, spiders, leaves bugs, you name it. It sounds like you need to identify the source of your malfunction, starting with a thorough inspection of the inside of the tank, the fuel strainer, lines, etc.
I am sorting this very problem out on an ancient 1987 Aero. Messy, nasty work. The good news is that I am finding valuable artefacts from pre-history encased in the Amber resin I am scooping out of the fuel system.
![Confused :?](./images/smilies/icon_confused.gif)
Stand by for my posts on this adventure.