[undy]

The Mallory Unilite uses an optical triggering system. The problem with that is as the engine runs there's some ozone creation inside the distributor cap. The ozone tends to "plate" out on the distributor's optical sensor over time. This continues until the generated optical light can't make it to the sensor. At that point you'll start to lose triggering and engine firing. Try cleaning your optics with some denatured alcohol. I had this problem many years ago with a Unilite myself.