NOS magnetos are often just as bad as magnetos that have been used for 40 or 50 years, the armature has a limited shelf life. Unlike dynamo's, these are often still ok.
Thanks for your advise. I change my plan to be focus on engine now so I postponed to concern on ignition system. I am preparing on understanding to remove the engine then learn to judge the performance/condition of crankshaft, fly wheel, roller bearing and other part near by of them.