I have questions but no answers. It's sunday and beautiful out side my 74 shovel is down now for two weeks. I put a new top end on it, rebuilt the carb, new coil,plugs,and wires. When I can get it started it runs good till it warms up then it pops and backfires. It has a crane cam hi-4 ignition in it. This is my second coil in it and now it seems that this coil has gone bad. What can I do and what could be the problem with the coils.