Generator giving single spark only?

So how do I test capacitor?

Without power in cap: Put multimeter in high ohms range and leads on the two wires from the cap. Your meter should slowly swing from 0 to infinity.
Some meters have a capacitance mode but most don't go high in value. What is the value of the capacitor? You could also list the Mfg (someone may have turned up a bad cap with that name).

Maybe I missed it, what instigated the board replacement and all the rest? Getting back to the "simplest may be the problem", you have checked that you have good battery power and all connections are continuous?