I do not have my 3 wheeler as of yet so I can not check the handbook or my theory
But as a thought, does the 2nd tank have any way to vent or release the air pressure in it? As you fill the 1st tank, the petrol flows to the 2nd tank through the connection at the bottom, but once it fills past that point it, could it be trapping a large air pocket in the 2nd tank?
Again, never seeing a new 3 wheeler in person, I haven't had the chance to inspect things for myself, and the internet videos don't show these parts in great detail.
