76 TR6 carb

Hey all, I have a 76 tr6 with twin sidedraft carbs 3 cylinders each.The engine runs ok but only uses the front carb. If I put my hand over the intake on the front carb the enge dies right away. If I put my hand over the intake on the rear carb port it does nothing almost like the rear carb is dead. Shouldn't both carbs be pulling the same amount of air in and if so what might be the issue?