OT as it's not a Landrover but I know there's lots of knowledge about propane fired engines in this group:
Hyster gas powered fork lift with Mazda engine starts easily, runs just long enough for me to back it out of the shed, then dies faltering first as though run out of gas. Lots of gas pressure, big fat juicey spark at the plugs, no sign of icing on the carb, but no firing what so ever when cranked. Leave it for half an hour and she fires up fine and runs all day long. It's happened twice recently with identical symptoms. Any suggestions?
AWEM