My engine will not turn help?

The lond pop is referred to as a backfire. That means you have fuel and spark, just not at the right place at the right time. It could be the spark plugs. Try taking one spark plug wire off and starting it. Do this on each spark plug one at a time and if there is one wire that you take off and it doesn't make a difference then thats the one with the problem. So it could be the Spark plug, The spark plug wire or even the distributor contact. Make sure to put the right wire back on the right spark plug. The wires should make a pop noise when they come off and a snap noise when they go back on and they should be firm fitting.