i have a 1971 mustang with a 351 cleavlend and it runs good but when accelerating it has little miss fires and when i get going above 20 and give it a bit of gas it seemes slugest. it makes noice but doesnt really throw you back in the seat like it use to. i put a new timing chain and cleaned the carb . it does have what lookes like the stock coil though. so can you help me out ?