I've melted Zinc and Zinc/Aluminum (die-cast) on a gasoline plumber's pot. It takes longer than Lead, but it will work. When you are heating up large chunks of metal in big pots you lose a lot of heat through air circulation. If you make yourself a wind shield around the pot it will speed up the heating. On windy days it's the only thing that will allow melting the Zinc/ Aluminum alloys. If you want to speed up your melting with the weed burner, try building a little shelter out of dry bricks. Put the pot on a couple of fire bricks to allow heat to get to the bottom. Be sure to allow for an airflow to allow the burned gasses to chimney away. Another possibility is to just dig a pit and allow the flame to warm the pot.
Old plumber's pots can occasionally be found rusting and covered with dust. They usually require a new leather in the pump and a cleaning of the gas generator. Rust in the tank is a bad sign. They were made to run on white gas, but I've run them on kerosene, parts cleaning solvent (Stoddard Safety), and Coleman fuel, or a mix of all three. Stay away from anything that will form charcoal in the generator, like vegetable oil or some blends of Diesel. Later models were propane fueled, and a little more energetic than turkey frying burners, but not as plentiful.
Nice picture BTW, showing the preheating of the mold.
