My son recently purchased a 1987 Intruder VS1400. It only runs on one cylinder. Not the spark plug and it gets gas. The one he bought it from said it needs a CDI box. Is there a way to test that to determine if it is indeed the CDI and if it is, where can he get one. We determined that it is an 8-4 and not the 6-4 plug. I know the CDI from the years of 87 to 93 are compatible.