A method to prevent fuel starvation when selecting aux tanks (inboards, also not fitted with electric pumps) was to select the aux tank in cruise one at a time and monitoring the fuel flow. Any reduction in flow required a reselection of the appropriate main (outboards,with electric pumps).
A second selection of the aux tank would then result in a vapourisation free flow. Worked for me 2000 hrs plus in the tropics.
