Well then if you had a serious backfire! it is quite possible you have unloaded the lifters!! it happened to that target master, she backfired hard and tore the skin of the muffler, unloaded lifters will not allow the valves to open properly, and will change with every crank! pull the intake and lifters soak them in a can of oil, for a day or so! or you can reload them with a manuel pump oil can. just an idea! might be the problem. Good Luck.