It sounds like a stuck float. You can try lightly tapping on the carbs with a screwdriver handle or small hammer. All you are trying to accomplish is to get the floats to free up. Some times this will loosen the float valves. Verify the floats releasing by just turning on the ignition switch, without starting the engine, and listen for the pump to stop running, it should not come back on again even after 1-2 minutes.
Hopes this helps.
Live to Ride, Ride to Live, Work to support Life