Hi, since it runs for a bit and then stops, check for fuel and vent-related causes first. When you had that carb open for cleaning and inspection, would gas freely flow when the float was down, and did it stop when the float was up? Did the float move freely?
Try running again with the gas cap loosened. Check that the float bowl is full of gas. Try both normal and reserve positions on the fuel petcock. If it won't even idle, the slow jet or enricher circuit could be clogged.
Where are you smelling for gas??Have spark but can't smell gas