There is a 70s blacksploitation movie that is very cheesy that has a large black woman as the lead. From what I remember her son was murder and she is going after the people who killed him. I want to say her sons name was Tyrone.
I can't find one that fits the limited information you provide. Some titles you might look at are Coffy (1973), Foxy Brown (1974), Cleopatra Jones (1973), T.N.T. Jackson (1974), Sugar Hill (1974), Sheba, Baby (1975), and Friday Foster (1975).