Anyone.
This tank thing that has been going on intrigues me, if the tank vent was under the fuel level and the fill line also, the only way to get air into the tank whilst the engine is not running is through the carb, now if you are filling the tank through the engine line, that would then be full of fuel when reconected to the carb, if the tank is higher than the carb, you have then got a perfect syhon to fill your carb with. A three pipe system would solve this by fill and empty through a vent line that is to the bottom of the tank, plugged after filling, the other vent to the top of the tank connected to the silencer, and engine line as normall to the clunk. The syphon effect could establish itself but only after fuel had been drawn through the carb line, if that line is positioned such that it has a route above the fuel upermost level the syphon cannot establish itself without a purposfull draw through the carb line. This is all thoughts that are occuring whilst I'm writting this, feel free to contradict if you need too.
Mike