Check your ignition wire resistence values (use a digital ohm meter), install a new set of plugs and have someone with the required skills set your carburetion and ignition timing. Additionally,with the symptom(s) exibiting themselves, observe coil firing via inductive pick-up timing light connected to the coil wire. Firing should be constant without any interruptions in pulse. Also, carburetor idle mixture as well as synchronization is crucial. Good luck.
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