You say the float bowls went dry .
Don't know how well versed you are with BMW airhead bikes, but you have to manually move the fuel tap lever, into the 6 o'clock position to get fuel to flow, there isn't a vacuum valve to do this, like a majority of bikes have .
The lever is in 'Reserve', if it is in the 12 o'clock position, and at either the 3 or 9 o'clock position, the fuel is shut off .