Fry salt pork in soup kettle until crisp. Remove with slotted spoon and set aside. Saute onions in fat until tender. Add potatoes, tomatoes, red pepper, thyme, and clam juice. Bring mixture to a boiL reduce heat, and simmer partially covered, 20 minutes. Add clams and cook 5 minutes longer. Season with salt and pepper. Garnish with reserved salt pork.