This is probably not the cure for your problem but worth bearing in mind anyway. After a few weeks the petrol in the carbs might have all evaporated away and the fuel pump seems to have a time limit control on continues operation. So when you first turn on the ignition wait for the pump to stop clicking (about 6 seconds), then turn off ignition for a few seconds and then on again. You might then hear more clicking and when it slows down rather than a sudden stop the carbs should be full. Now start to crank the engine.
Some times using the cold start lever to maximum can flood the engine, so maybe experiment with that a bit.