So long as the fuel delivery system system is working as it should then it's all old technology that has to be addressed.
Spark plugs,plug caps and HT leads and the the coils all of which are over 150 years old as far as Internal combustion engines are concerned still have to deliver the spark to the cylinder.There's not been a lot of innovations in these components but the tolerances and materials used has improved of course over the years but if any of then grow weak or are failing there will be problems.
The correct values for the coils are in my Haynes in the checking procedure.Not checked the downloaded Manual but I'm sure they are in there as well.
I found and promoted a cheap coil alternative for my CX500s CDI coils and I'm sure the SV650's are just a dual tap car version.
I got my Haynes from Halfrauds.Got 2 quid off as the cellophane cover was damaged