Some very good suggestions already it seems.

I became heavily involved in these troubles with Dave's F15 Polsten and it is reported way back in previous posts.

Vapour locks occur on the inlet or suction side of the pump, whilst it was problematical when built, it is far worse now with high volatility fuel designed for injected engines; octane and volatility are not to be confused, AVGAS is high octane but low volatility to alleviate these situations and carb icing also. (see Reid Vapour Pressure)

The engine layout is ideal for substantially heating the fuel pump and the inlet fuel line, this starts the vapourisation process and the pump trying to draw fuel by creating a vacuum just lowers the boiling point further creating a vicious circle.

You will not get vapour in the output line as the pump pressure, provided it has liquid fuel supplied, increases the boiling point.

The original factory modification was a switchable (from the dash) electric pump (The Autopulse) located behind the battery at the back of the driver's step and effectively gravity fed. This kept some positive pressure to the mechanical pump inlet and was a standard fit to all these trucks being operated in hot/desert climates.

Dave and I decided to simplify the whole system for reliability after all the troubles you are having even in the cooler climate of the UK but probably with even more volatile, anti-pollution specified, EU standard fuel.

The mechanical pump has no push-rod fitted and the valves removed, the diaphragm remains just as a seal and the whole fuel supply is done by a 6V Facet pump located where the Autopulse would be. This cured all the fuel supply issues.

You'll still get the hot start difficulty as the carb is cooked by engine heat once stopped and simply percolates most of the fuel from the float bowl straight out of the main jets and quickly makes the engine totally flooded.

There is no absolute cure for this but four things can help a great deal.

Ditch the terrible Ford ignition coil and its ballast resistor (by just taking one wire to the other end) then use a modern 6V coil, the original can be left with dummy wiring for aesthetics.

Use decent modern, big name spark plugs, I think its NGK B6 for this engine. The B6M is common being a shortened insulator version for lawn mowers!

Ensure the battery is adequately rated and in good order; use the biggest cable possible with soldered lug connections from the battery to solenoid and then starter, don't forget the huge starting current has to flow back as well and the same size is needed from the engine back to the battery too. Standard 12V car size starter cable will not do. We saw an extra 1.25V at the starter by replacing these cables.

Employ a hot start technique, you know it will be flooded; open the throttle 1/3rd to 1/2, hold it there and crank it until it fires then slowly back the throttle keeping the revs up for a few seconds until its cleared itself.

R.