Here are some links to useful information about the ignition problems you are encountering. The symptom you describe sounds like one of the two cdi power coils on the stator coil is kaput (the high speed one-- see the link from uk and the "white wire fix" for high speed coil problems).
I wouldnt give up on the bike. Engine removal from the frame is not a killer job- one summer afternoon and a decent hydraulic bottle jack. The electrex G47 replacement stator coil is quite reliable and at $150 fob america from electrex uk is a good deal. Same coil ordered from electrex usa is $225. Check out electrex uk.
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