Motorcycle Repair: 1978 cb400 hawk weak spark, honda hawk, open circuits

Question
I have a 1978 honda hawk with weak spark. the motor blew up and I bought it with intentions of rebuilding it and riding. I finished rebuilding the motor and it woudlnt start. I took the plugs out to check for fire and the plugs are firing so weak the electrode has to be about a hair's width away from the ground to fire at all it wont fire with the ground on the plug the gap is too large. have you seen this before? Any idea what could be causing it?

Answer
There are several things to check for the cause of weak spark. Check the battery for charge and strength, check the ignition coil(s) for open circuits, check the CDI box, the spark plug cables and the spark plugs themselves. Any of these components could require replacing. There is no easy method to check all these parts other than to replace each one until the problem is solved, so it can get pricey and time consuming. Given the age of the bike, it probably needs new spark plugs and wires anyway, so change those first. If the problem is still there, it is most likely the coil or CDI at fault.