Carbs only leak fuel when there is a problem
with the float, needle valve under the float
or plugged float bowl vents or overflow tube.
What likely occurred is that you have some bad
stuff coming down the fuel lines from the tank
or a faulty petcock or bad fuel hose.
Without a good fuel filter inline the float valves
will immediately start to stick and leak fuel.
The float valves have to be in perfect condition
and the seat has to be very clean as well.
Some needle valves have orings on them
which can also leak fuel into the bowl making
If any fuel runs from the carbs when the bike
is not running then the float needles are leaking.
If you have a vacuum petcock it could be faulty
and may be allowing raw fuel to be pulled into the engine
through the vacuum hose.
Even if they were just cleaned the carbs have to have
an external fuel filter or they will cause problems
immediately and have to be cleaned again, at least
the float valves.