That's a Duraspark II. A pretty dependable system. They generally work or they don't. Ya could try a new coil. And take the Module to like Autozone and have it tested. There are guy's here that can tell ya how to test the coil with a multi-meter.

How is the spark at the plugs when it is hard to start? Maybe check the spark when cold than hot and compare it. Spark should be blue and snap and jump a long way.