scale model engines running on propane

[Harglo]

Any one have a feel for what size tubing to use form regulator an then form the demand valve/s to the carb? Been using 1/8" ID but some times engine will run for 15-20 minutes an stops restarts ok. Em using two of the 1lb throw away tanks. Does one need larger or smalle tubing incase that's the problem? Tubing lines have to be about 2 feet long as run 2- 3 engines from propane station.
Harvey