Wolf Power 800?

I have one of the above generators, with no spark at the plug or end of HT lead. I have cleaned the inside of the flywheel and ends of the pick-up coils, checked the wires from these coils for continuity all ok. I can't check the little black box, which I think has some kind of condencer unit inside, as it is sealed. So I am wondering if it is this box or the HT coil at fault