Retarded set-up, 18cc domes and stock pipes?
Start at ground zero. Get a Clymers repair manual, ohm ALL elec, coil ground, clean/tight elec connections, carb slides, carb sync, carb settings, new PROPER plugs.
How are reeds? Fresh fuel, or same fuel from 10yrs ago? Mix ratio?
What kind of compression are you running?
Fucking with the same problem for 10 yrs?? You surely jest.