It is doing a number of wierd stuff maybe someone here with expertise can lend some insight. First it has trouble with cold starts. i have to keep my foot on the pedal to keep it from turning off. after like 30 seconds of having my foot on there the car will stay on by itself. now i can drive the car with no problem when i first turn it on. this is the part where i get problems once the car gets up to normal operating temperature the carb will start to backfire like crazy and the car is virtually impossible to drive. it will back fire so much that the car eventually turns off on me. that very moment when the car turns off it will not turn on anymore unless i have the gas pedal to the ground. then only will it turn on but not completely it feels as though the exhaust is clogged up. my muffler will make a rattling noise like there is something loose in there and then all of a sudden the car frees up and throws a bunch of black smoke out the tail pipes and the car stays on but once again backfires if i try to drive it. it almost feels like the motor is building up internally and then suddenly releases all its power through the exhaust. it is not a continuous flow like it was in the begining. mind that the car is a 83 5.0 H.O car it still has the 4180 holley carb it came with and it is stick shift. can anyone guess what the heck is going on?? it has a new fuel pump and has had a recent tune up spark plugs, wires, cap, rotor fuel filter, air and oil, thanks anyways!