Even though the tap was off, it doesn't mean that the float needle hadn't stuck previously and allowed the carb to overflow and drain into the chamber. It can take a while for fuel in an expansion chamber to evaporate, so could've been in there for a while.

You'd need to either be running huge carbs and jets and have a misfire or poor starting on one cylinder, or have a stuck float valve to fill the chamber up really. Think about it logically... there's only one place the fuel can come from... the carb! If the tap doesn't leak, then it must be a float level/valve issue or it's not burning all the fuel you are feeding into the crankcases.
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Andy.
NSR-WORLD.COM

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