So many possibilities...coil getting hot, condenser, cracks in the dizzy cap,failing plug leads, air leaks in the inlet manifold. Check for plug lead failure -run it in the dark looking for visible sparks, or , one lead at a time off the car, meter across the ends, twirl the wire like a skipping rope, looking for the meter reading to change. When its hot, spray something lightly flammable (thin oil?) on all the joints on the carb and the inlet, looking for a change in engine note. Inspect and clean the inside of the dizzy cap and the rotor for cracks or carbon dust tracks. The coil can get warm, but should not get so hot you cant hold it . Any sign of oil in the coolant,indicating a head gasket problem - coolant looks like milk coffee,or has visible oil drops in it? Is the choke fully home (off) when its lumpy? is the air cleaner OK, not clogged? Do you know the revs at the time? Does it drive ok generally, and when the idle is lumpy?