What a pity for ignorance, the connection to the overflow valve is the same as the vent? or where it is located.Use a wire to ensure the tank vent is not plugged, it's a very small opening.
Did you have the jet block rubber plugs in the wrong places? I bought a used bike, and I didn't even try starting it before I tore-down the carburetors. I found one of the jets wasn't even screwed-in the jet block.