In a large saucepan, simmer the pork, marjoram, thyme and bay leaves in 4 cups of salted water, partially covered, until the meat is tender, 45 minutes. Using a slotted spoon, transfer the pork to a plate; let cool slightly, then tear it into smaller pieces. Skim the fat from the pork broth; reserve 1 1/2 cups.
In a large saucepan of boiling salted water, cook the potatoes until just tender, about 8 minutes. Drain well.
In a medium, deep skillet, heat the oil. Add the chorizo and stir over moderately low heat, breaking it up, until cooked through, 10 minutes; transfer to a plate. Add the pork and onion to the skillet and cook over moderate heat, stirring, until well-browned, 10 minutes. Add the garlic and cook for 1 minute. Stir in the tomatoes and chorizo and cook for 5 minutes. Add the potatoes, chipotle, adobo sauce and the 1 1/2 cups of pork broth; simmer for 10 minutes. Season with salt and a pinch of sugar and serve.