Add pork and remaining ingredients to a large pot, cover with water. Season with salt to taste and bring to a boil. Reduce to a simmer and continue cooking, mostly covered for 4 hours. Skim foam off the top as needed and turn as needed. After liquid reduces halfway through cooking time, add enough water to just cover pork and continue cooking.
Remove pork from hot stock. Let cool slightly and then remove the meat from the bone. Transfer to a storage container and cover with just enough pork stock to cover the meat. Let cool at room temperature. Skim the fat off the remaining pork stock. Strain out the solids and discard. Once cooled you can freeze the stock for future recipes.
To finish shredded carnitas, add pork with stock to pot and bring to a boil, reduce heat and continue cooking, stirring as needed until liquid reduces by 3/4. Add juice of 1 lemon, 1 orange, chile de arbol powder, garlic powder, pepper and salt to taste. Reduce until all the liquid has evaporated.
Add 2 full tablespoons of manteca and cook on high heat to crisp and brown the pork. Shred with two forks if needed.